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From Many Divides, One? The Polarization and Nationalization of American State Party Platforms, 1918–2017

Published online by Cambridge University Press:  07 March 2022

Daniel J. Hopkins*
Department of Political Science, University of Pennsylvania, Philadelphia, Pennsylvania, USA
Eric Schickler
Department of Political Science, University of California, Berkeley, California, USA
David L. Azizi
Independent Researcher, Philadelphia, Pennsylvania, USA
Corresponding author: Daniel J. Hopkins, Email:


Many contend that U.S. state parties are increasingly polarized and nationalized, meaning that they have adopted divergent positions matching their national counterparts’ positions. Such trends reflect a transformation of America's historically decentralized party system. Yet, the precise timing of these related trends—as well as the mechanisms underpinning them—remain unclear. We assess these dynamics using a novel data set of 1,783 state party platforms between 1918 and 2017. Applying tools from automated and manual content analysis, we document a dramatic divergence in the topics emphasized by Democrats and Republicans starting in the mid-1990s, just as congressional speech became polarized. During this period, cross-state differences in each party's agenda decreased and regional/sectoral issues became less prominent, suggesting tight connections between polarization, nationalization, and state agendas. We also find that innovative phrases increasingly debut in state (not national) platforms. Overall, the evidence undercuts claims of top-down polarization emanating from national party leaders in Washington, DC. Polarization at the state and federal levels coincided with the development of an integrated network of activists spanning multiple levels of the polity.

Research Article
Copyright © The Author(s), 2022. Published by Cambridge University Press

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1 Nolan McCarty, Polarization: What Everyone Needs to Know® (Oxford, UK: Oxford University Press, 2019).

2 For important recent exceptions, see Grumbach, Jacob M., “From Backwaters to Major Policymakers: Policy Polarization in the States, 1970–2014,” Perspectives on Politics 16, no. 2 (2018): 416–35CrossRefGoogle Scholar; Rocco, Philip, Kelly, Andrew S., and Keller, Ann C., “Politics at the Cutting Edge: Intergovernmental Policy Innovation in the Affordable Care Act,” Publius: The Journal of Federalism 48, no. 3 (2018): 425–53CrossRefGoogle Scholar; Alex Hertel-Fernandez, State Capture: How Conservative Activists, Big Businesses, and Wealthy Donors Reshaped the American States—and the Nation (Oxford, UK: Oxford University Press, 2019); Béland, Daniel, Rocco, Philip, and Waddan, Alex, “The Affordable Care Act in the States: Fragmented Politics, Unstable Policy,” Journal of Health Politics, Policy and Law 45, no. 4 (2020): 647–60CrossRefGoogle ScholarPubMed; Bucchianeri, Peter, “Party Competition and Coalitional Stability: Evidence from American Local Government,” American Political Science Review 114, no. 4 (2020): 1055–70CrossRefGoogle Scholar; Devin Caughey and Christopher Warshaw, Dynamic Democracy: Citizens, Parties, and Policymaking in the American States, 1936–2016 (Chicago: University of Chicago Press, 2022).

3 David B. Truman, “Federalism and the Party System,” in American Party Politics: Essays and Readings, ed. Donald G. Herzberg (New York: Holt, Rinehart & Winston, 1966).

4 Richard M. Valelly, Radicalism in the States (Chicago: University of Chicago Press, 1989).

5 Nelson W. Polsby, “The American Party System,” in The New Federalist Papers: Essays in Defense of the Constitution, ed. Alan Brinkley, Nelson W. Polsby, Kathleen M. Sullivan (Washington, DC: Brookings Institution Press, 1997).

6 Elmer E. Schattschneider, Party Government (New York: Farrar and Rinehart, 1942); see also Arceneaux, Kevin, “Does Federalism Weaken Democratic Representation in the United States?Publius: The Journal of Federalism 35, no. 2 (2005): 297–311CrossRefGoogle Scholar. In Party Government, Schattschneider argues that “decentralization of power is by all odds the most important single characteristic of the American major party.… [It] is … a loose confederation of state and local bosses for limited purposes.” Though a less forceful advocate of party government than Schattschneider, the pluralist Truman states that “the basic political fact of federalism is that it creates separate, self-sustaining centers of power, privilege, and profit … as means of leverage upon elements in the political structure above and below” (Truman, “Federalism and the Party System,” 30). Truman concludes that the American party system is “structurally unstable and disjointed” (26). Mickey offers a powerful account of the normative shortcomings of America's decentralized parties: They allowed for a set of authoritarian, one-party enclaves in the South that were embedded in, yet largely autonomous from, both the national party and the national government. In Mickey's account, a more nationalized polity was essential for democratization of the South. Robert Mickey, Paths Out of Dixie: The Democratization of Authoritarian Enclaves in America's Deep South, 1944–1972 (Princeton, NJ: Princeton University Press, 2015).

7 Shor, Boris and McCarty, Nolan, “The Ideological Mapping of American Legislatures.The American Political Science Review 105, no. 3 (2011): 530–51CrossRefGoogle Scholar; Matt Grossmann, Red State Blues: How the Conservative Revolution Stalled in the States (Cambridge, UK: Cambridge University Press, 2019); McCarty, Polarization; Caughey and Warshaw, Dynamic Democracy.

8 See also Eric Schickler, Racial Realignment (Princeton, NJ: Princeton University Press, 2016); Matthew A. Carr, Gerald Gamm, and Justin H. Phillips, “Origins of the Culture War: Social Issues in State Party Platforms, 1960–2014” (paper prepared for presentation at the annual meeting of the American Political Science Association, Philadelphia, PA, September 2016),; Daniel Hopkins, The Increasingly United States (Chicago: University of Chicago Press, 2018).

9 But see Grumbach, “From Backwaters.”

10 Richard Franklin Bensel, Sectionalism and American Political Development, 1880–1980 (Madison: University of Wisconsin Press, 1984).

11 James G. Gimpel, National Elections and the Autonomy of American State Party Systems (Pittsburgh, PA: University of Pittsburgh Press, 1996); James G. Gimpel and Jason E. Schuknecht, Patchwork Nation: Sectionalism and Political Change in American Politics (Ann Arbor: University of Michigan Press, 2003); Joel W. Paddock, State & National Parties & American Democracy (New York: Peter Lang, 2005); Shor and McCarty, “Ideological Mapping”; Daniel J. Coffey, “Federal Parties and Polarization,” in The State of the Parties (Lanham, MD: Rowman & Littlefield, 2014); Caughey, Devin and Warshaw, Christopher, “The Dynamics of State Policy Liberalism, 1936–2014,” American Journal of Political Science 60, no. 4 (2016): 899–913CrossRefGoogle Scholar; Caughey, Devin, Warshaw, Christopher, and Xu, Yiqing, “Incremental Democracy: The Policy Effects of Partisan Control of State Government,” The Journal of Politics 79, no. 4 (2017): 1342–58CrossRefGoogle Scholar; Caughey, Devin, Dunham, James, and Warshaw, Christopher, “The Ideological Nationalization of Partisan Subconstituencies in the American States,” Public Choice 176, no. 1 (2018): 133–51CrossRefGoogle Scholar; Grumbach, “From Backwaters.”

12 David M. Blei, Andrew Y. Ng, and Michael I. Jordan, “Latent Dirichlet Allocation,” Journal of Machine Learning Research 3 (2003): 993–1022.

13 Shor and McCarty, “Ideological Mapping.”

14 Carmines, Edward G. and Stimson, James A., “The Two Faces of Issue Voting,” American Political Science Review 74, no. 1 (1980): 78–91CrossRefGoogle Scholar; Hopkins, The Increasingly United States. A related question is whether there are important asymmetries between the parties, such as Grossmann and Hopkins's national-level observation that Democrats tend to focus more on appeals to specific groups, while Republicans tend to focus on abstract, ideological appeals; Matt Grossmann and David A. Hopkins, Asymmetric Politics: Ideological Republicans and Group Interest Democrats (New York: Oxford University Press, 2016).

15 See also Daniel M. Butler and Joseph L. Sutherland, “Have State Policy Agendas Become More Nationalized?” (working paper, under review; available upon request),; Sanmay Das, Betsy Sinclair, Steven W. Webster, and Hao Yan, “All (Mayoral) Politics Is Local?” Journal of Politics (forthcoming).

16 See also Schickler, Racial Realignment.

17 Jonathan Bernstein, “The New Presidential Elite,” in In Pursuit of the White House 2000 (New York: Chatham House, 2000); Marty Cohen, David Karol, Hans Noel, and John Zaller, The Party Decides: Presidential Nominations Before and After Reform (Chicago: University of Chicago Press, 2009); Seth Masket, No Middle Ground: How Informal Party Organizations Control Nominations and Polarize Legislatures (Ann Arbor: University of Michigan Press, 2011); Bawn, Kathleen, Cohen, Martin, Karol, David, Masket, Seth, Noel, Hans, and Zaller, John, “A Theory of Political Parties: Groups, Policy Demands and Nominations in American Politics,” Perspectives on Politics 10, no. 3 (2012): 571–97CrossRefGoogle Scholar; Heaney, Michael T., Masket, Seth E., Miller, Joanne M., and Strolovitch, Dara Z., “Polarized Networks: The Organizational Affiliations of National Party Convention Delegates,” American Behavioral Scientist 56, no. 12 (2012): 1654–76CrossRefGoogle Scholar; Cohen, Marty, Karol, David, Noel, Hans, and Zaller, John, “Party Versus Faction in the Reformed Presidential Nominating System,” PS: Political Science & Politics 49, no. 4 (2016): 701–708Google Scholar; Sam Rosenfeld and Daniel Schlozman, “The Hollow Parties,” in Can America Govern Itself? (Cambridge, UK: Cambridge University Press, 2019): 120–44.

18 As discussed below, however, it leaves quite open the possibility that national networks—such as the American Legislative Exchange Council (ALEC) on the right—seed these new frames and positions as the state-level and then push for their diffusion across states and levels of government (see Hertel-Fernandez, State Capture).

19 David Karol, Red, Green, and Blue: The Partisan Divide on Environmental Issues, Elements in American Politics (Cambridge University Press [online], 2019), accessed December 15, 2020,

20 Gentzkow, Matthew, Shapiro, Jesse M., and Taddy, Matt, “Measuring Group Differences in High-Dimensional Choices: Method and Application to Congressional Speech,” Econometrica 87, no. 4 (2019): 1307–40CrossRefGoogle Scholar. In fact, on some social issues, the state parties may have led the national agenda, as detailed by Carr et al., “Origins of the Culture War.”

21 David R. Mayhew, Placing Parties in American Politics: Organization, Electoral Settings, and Government Activity in the Twentieth Century (Princeton, NJ: Princeton University Press, 1986).

22 Bawn et al., “A Theory of Political Parties”; Julia R. Azari, “Weak Parties, Strong Partisanship” (presentation at the Annual Meeting of the American Political Science Association, Boston, MA, 2018); Rosenfeld and Schlozman, “The Hollow Parties”; but see Daniel J. Galvin, Presidential Party Building (Princeton, NJ: Princeton University Press, 2010).

23 Truman, “Federalism and the Party System,” 25.

24 V. O. Key, Politics, Parties, & Pressure Groups (New York: Crowell, 1964), 315.

25 Schattschneider, Party Government.

26 Polsby, “American Party System,” 20.

27 Ibid. For the view that state and local party units enjoy considerable autonomy, see also Samuel J. Eldersveld, Political Parties: A Behavioral Analysis (Chicago: Rand McNally, 1964). Bensel (in Sectionalism) highlights the role of sectionalism as a foundational element in American politics, reinforcing patterns of decentralization rooted in the distinct political economies that constitute the U.S. system.

28 Shor and McCarty, “Ideological Mapping.”

29 McCarty, Polarization; Caughey and Warshaw, Dynamic Democracy.

30 Bryan D. Jones and Frank R. Baumgartner, The Politics of Attention: How Government Prioritizes Problems (Chicago, IL: University of Chicago Press, 2005).

31 Larry M. Bartels, “Electoral Continuity and Change, 1868–1996,” Electoral Studies 17, no. 3 (1998): 301–26; see also William Claggett, William Flanigan, and Nancy Zingale, “Nationalization of the American Electorate,” The American Political Science Review 78, no. 1 (1984): 77–91; Donald E. Stokes, “Parties and the Nationalization of Electoral Forces,” in The American Party Systems: Stages of Political Development, ed. W. N. Chambers and W. D. Burnham (New York: Oxford University Press, 1967); David W. Brady, Robert D'Onofrio, and Morris P. Fiorina, “The Nationalization of Electoral Forces Revisited,” in Continuity and Change in House Elections, ed. D. W. Brady, J. F. Cogan, and M. P. Fiorina (Stanford: Stanford University Press, 2000), 130–48; Mark P. Jones and Scott Mainwaring, “The Nationalization of Parties and Party Systems: An Empirical Measure and an Application to the Americas,” Party Politics 9, no. 2 (2003): 139–66; Daniele Caramani, The Nationalization of Politics: The Formation of National Electorates and Party Systems in Western Europe (New York: Cambridge University Press, 2004); Steven Rogers, “Electoral Accountability for State Legislative Roll Calls and Ideological Representation,” American Political Science Review 111, no. 3 (2017): 555–71; Hopkins, The Increasingly United States; Justin de Benedictis-Kessner and Christopher Warshaw, “Accountability for the Economy at All Levels of Government in United States Elections,” American Political Science Review 114, no. 3 (2020): 660–76.

32 But see Butler and Sutherland, “Have State Policy Agendas Become More Nationalized?”

33 In Patchwork Nation, Gimpel and Schuknecht show that the composition of the Democratic and Republican parties’ electoral coalitions differs significantly across states, with important consequences for party positioning and cleavages (see also Gimpel, National Elections). These contrasting electoral bases are a potent obstacle to nationalization in Gimpel and Schuknecht's account. In a similar vein, David Hopkins reports substantial and persistent state-to-state differences in political preferences; David A. Hopkins, Red Fighting Blue: How Geography and Electoral Rules Polarize American Politics (Cambridge, UK: Cambridge University Press, 2017). See also James G. Gimpel, Nathan Lovin, Bryant Moy, and Andrew Reeves, “The Urban-Rural Gulf in American Political Behavior,” Political Behavior 42 (2020): 1343–68.

34 There were earlier eras as well in which national parties gained greater sway over state parties and campaign strategy (e.g., on nationalizing changes adopted in the 1880s–90s; see Daniel Klinghard, The Nationalization of American Political Parties, 1880–1896 (New York: Cambridge University Press, 2010).

35 Pradeep Chhibber and Ken Kollman, The Formation of National Party Systems: Federalism and Party Competition in Canada, Great Britain, India, and the United States (Princeton, NJ: Princeton University Press, 2004).

36 Valelly, Radicalism in the States.

37 Gimpel, National Elections.

38 Mayhew, Placing Parties in American Politics.

39 Mickey, Paths Out of Dixie; John H. Aldrich and John D. Griffin, Why Parties Matter: Political Competition and Democracy in the American South (Chicago: University of Chicago Press, 2018).

40 Chhibber and Kollman, Formation of National Party Systems; Jacob T. Levy, “Federalism, Liberalism, and the Separation of Loyalties,” American Political Science Review 101, no. 3 (2007): 459–77; Richard Johnston, The Canadian Party System: An Analytic History (Vancouver, BC: UBC Press, 2017).

41 Chhibber and Kollman, Formation of National Party Systems.

42 John S. Jackson III and Robert A. Hitlin, “The Nationalization of the Democratic Party,” Western Political Quarterly 34, no. 2 (1981): 270–86; Leon D. Epstein, “Party Confederations and Political Nationalization,” Publius 12, no. 4 (1982): 67–102. Although the national GOP did not impose a similar set of procedural regulations on its state parties, the Republican presidential nomination process ended up changing, as many state legislatures responded to McGovern-Fraser by approving new primary laws that applied to both parties.

43 John F. Bibby, “Political Parties and Federalism: The Republican National Committee Involvement in Gubernatorial and Legislative Elections,” Publius 9, no. 1 (1979): 229–36; M. Margaret Conway, “Republican Political Party Nationalization, Campaign Activities, and Their Implications for the Party System,” Publius: The Journal of Federalism 13, no. 1 (1983): 1–17; Epstein, “Party Confederations.”

44 Joel W. Paddock, “Local and State Political Parties,” in The Oxford Handbook of State and Local Government, ed. Donald P. Haider-Markel (Oxford University Press, 2014), 164–88, doi:10.1093/oxfordhb/9780199579679.001.0001; see also John H. Aldrich, Why Parties? A Second Look (Chicago: University of Chicago Press, 2012).

45 See Robert J. Huckshorn, James L. Gibson, Cornelius P. Cotter, and John F. Bibby, “Party Integration and Party Organizational Strength,” The Journal of Politics 48, no. 4 (1986): 976–91; Andrew M. Appleton and Daniel S. Ward, “Party Response to Environmental Change: A Model of Organizational Innovation,” Party Politics 3, no. 3 (1997): 341–62.

46 William M. Lunch, The Nationalization of American Politics (Oakland: University of California Press, 1987); Paddock, State & National Parties; Daniel J. Coffey, “State Party Activists and State Party Polarization,” in The State of the Parties: The Changing Role of Contemporary American Parties, ed. John C. Green, Daniel J. Coffey, and David B. Cohen (Lanham, MD: Rowman & Littlefield, 2007); Hans Noel, Political Ideologies and Political Parties in America (New York: Cambridge University Press, 2014); Hertel-Fernandez, State Capture; Eitan Hersh, Politics Is for Power: How to Move Beyond Political Hobbyism, Take Action, and Make Real Change (New York: Simon and Schuster, 2020).

47 See John H. Aldrich, “A Downsian Spatial Model with Party Activism,” The American Political Science Review 77, no. 4 (1983): 974–90.

48 See Hertel-Fernandez, State Capture; but see Grossmann, Red State Blues.

49 Schickler, Racial Realignment.

50 John W. Soule and James W. Clarke, “Amateurs and Professionals: A Study of Delegates to the 1968 Democratic National Convention,” The American Political Science Review 64, no. 3 (1970): 888–98; Carl Everett Ladd Jr. and Charles Hadley, Transformations of the American Party System, 2nd ed. (New York: Norton, 1978); Byron E. Shafer, Bifurcated Politics: Evolution and Reform in the National Party Convention (Cambridge, MA: Harvard University Press, 1988); Geoffrey C. Layman, Thomas M. Carsey, John C. Green, Richard Herrera, and Rosalyn Cooperman, “Activists and Conflict Extension in American Party Politics,” American Political Science Review 104, no. 2 (2010): 324–46.

51 Paddock, State & National Parties.

52 Mayhew, Placing Parties in American Politics.

53 Danny Hayes and Jennifer Lawless, “How Uncompetitive Elections and Media Consolidation Impoverish the News and Diminish Democracy” (paper presented at the Midwest Political Science Association, Chicago, IL, 2014); Hopkins, The Increasingly United States; Matthew S. Levendusky, “How Does Local TV News Change Viewers’ Attitudes? The Case of Sinclair Broadcasting” Political Communication 39, no.1 (2021): 23–38; Daniel J. Moskowitz, “Local News, Information, and the Nationalization of U.S. Elections,” American Political Science Review (2020): 1–16; Danny Hayes and Jennifer Lawless, News Hole (Cambridge, UK: Cambridge University Press, 2021).

54 Joshua P. Darr, Matthew P. Hitt, and Johanna L. Dunaway, “Newspaper Closures Polarize Voting Behavior,” Journal of Communication 68, no. 6 (2018): 1007–28.

55 Gregory J. Martin and Joshua McCrain, “Local News and National Politics,” American Political Science Review 113, no. 2 (2019): 372–84.

56 Yphtach Lelkes, Gaurav Sood, and Shanto Iyengar, “The Hostile Audience: The Effect of Access to Broadband Internet on Partisan Affect,” American Journal of Political Science 61, no. 1( 2017): 5–20.

57 See Azari, “Weak Parties, Strong Partisanship”; Rosenfeld and Schlozman, “The Hollow Parties.”

58 See, e.g., Carmines and Stimson, “Two Faces of Issue Voting”; Geoffrey C. Layman and Thomas M. Carsey, “Party Polarization and ‘Conflict Extension’ in the American Electorate,” American Journal of Political Science 46, no. 4 (2002): 786–802; Ashley E. Jochim and Bryan D. Jones, “Issue Politics in a Polarized Congress,” Political Research Quarterly 66, no. 2( 2013): 352–69; Daniel Schlozman, When Movements Anchor Parties: Electoral Alignments in American History (Princeton, NJ: Princeton University Press, 2015); Carr et al., “Origins of the Culture War”; Hopkins, Red Fighting Blue.

59 Note that a decentralized party system may create opportunities for movements to raise the salience of social issues that the national parties have incentives to avoid. For example, McConnaughy's study of women's suffrage demonstrates that movement activists first built successful coalitions at the state level, capitalizing on particular state parties’ need to appeal to allied interest groups (e.g., the Grange in Michigan, which became a key supporter of women's suffrage in 1911); Corrine M. McConnaughy, The Woman Suffrage Movement in America: A Reassessment. (Cambridge, UK: Cambridge University Press, 2013). These state-level gains eventually tilted the balance in favor of a democratizing reform at the national level as well.

60 Observers have also noted key asymmetries in the two major political parties, with the Republican Party sometimes characterized as more organizationally centralized, top-down in structure, and ideologically homogeneous (Galvin, Presidential Party Building; Grossmann and Hopkins, Asymmetric Politics; Hertel-Fernandez, State Capture). In part, such differences may be grounded in electoral geography, as the interplay of America's electoral institutions and the spatial distribution of partisan support requires the Democrats to win a wider variety of districts to win power nationally; Jonathan Rodden, “The Geographic Distribution of Political Preferences,” Annual Review of Political Science 13 (2010): 321–40; Hopkins, Red Fighting Blue. It is possible, then, that Democratic agendas will show more heterogeneity, but also more over-time change as politics nationalizes.

61 Schickler, Racial Realignment.

62 David Karol, Party Position Change in American Politics: Coalition Management (New York: Cambridge University Press, 2009).

63 Butler and Sutherland (“Have State Policy Agendas Become More Nationalized?”) rely on governors’ State of the State Addresses as an alternative indicator of party positioning and emphasis. Studying the period from 1960 to 2016, they find that states’ agendas grew increasingly similar to other states’ as well as to presidential State of the Union addresses. However, such results are limited as measures of polarization because only the party that holds the governor's seat delivers an address.

64 Brian D. Feinstein and Eric Schickler, “Platforms and Partners: The Civil Rights Realignment Reconsidered,” Studies in American Political Development 22, no. 1 (2008): 1.

65 Richard F. Bensel, The Political Economy of American Industrialization, 1877–1900 (Cambridge, UK: Cambridge University Press, 2000); Adam Silver, “Consensus and Conflict: A Content Analysis of American Party Platforms, 1840–1896,” Social Science History 42, no. 3 (2018): 441–67; Adam Silver, “Elites and Masses: The Prevalence of Economics and Culture in Nineteenth-Century American Party Platforms,” American Nineteenth Century History 20, no. 1 (2019): 41–64. Bensel finds the greatest party unity on the tariff, arguably the central issue dividing Democrats from Republicans, but identifies considerable diversity in state party positioning on other economic issues, such as the currency and corporate regulation. This diversity generally reflected regionally based variation in political-economic interests and cleavages.

66 Joel Paddock, “Inter-Party Ideological Differences in Eleven State Parties: 1956–1980,” Western Political Quarterly 45, no. 3 (1992): 751–60; Paddock, State & National Parties.

67 A further question is what predicts which state parties are more extreme. In “State Party Activists,” Coffey finds that a standard measure of state-level liberalism in the mass public is not associated with the relative liberalism of each party's platform. Instead, Coffey's measure of state activist opinion is related to platform liberalism. State activist ideology is measured by the pooled average ideology of its delegation to the four national conventions held from 1992 to 2004. In “Federal Parties and Polarization,” Coffey finds modest geographic diversity, with Democrats a bit less liberal in the South, but even so, Southern Democratic state parties are well to the left of the most liberal GOP state parties.

68 See also Paddock, State & National Parties.

69 Carr et al., “Origins of the Culture War.”

70 Ibid.; Schickler, Racial Realignment.

71 Paddock, State & National Parties; Feinstein and Schickler, “Platforms and Partners”; Coffey, “Federal Parties and Polarization”; Carr et al., “Origins of the Culture War”; Paul Lendway and John Henderson, “The Rise of Tea Partism in State Party Platforms” (working paper, Yale University, New Haven, CT, 2020).

72 We are grateful to Daniel Coffey, Brian Feinstein, Daniel Galvin, Gerald Gamm, John Henderson, Joel Paddock, and Justin Phillips for their willingness to exchange platforms.

73 As part of an agreement with our partners, 155 post-1960 but pre-2000 platforms will be released at a later date upon the completion of a separate research project. All of the quantitative data and code used in our empirical analyses will be released upon publication.

74 Aldrich and Griffin, Why Parties Matter. The lower platform coverage in the South is a product of the less developed formal party organizations in the region, particularly prior to the era of two-party competition that took hold in the 1950s–60s (Key, Politics, Parties, & Pressure Groups). In the era of one-party competition, the absence of a viable GOP organization often meant that the party did not even write a platform. Even when platforms were written, however, the record-keeping tended to be weaker than elsewhere. In thinking about the share of platforms we obtained, our examination of party records indicates that the typical northern state party wrote a platform every other year (a handful of states at times wrote platforms every year, while others did so every four years, but the norm was biennial). This suggests that we obtained approximately 43 percent of the platforms written in these thirty-nine states during this period (1,557 out of 3,640). In total, we obtained 226 platforms for the eleven states of the South; even with the lower rate of platform-writing in those states prior to the 1960s, our ability to obtain southern platforms was clearly more limited. If one focuses on 1964 to 2017—when two-party competition makes it more likely that Democrats and Republicans regularly wrote platforms in each Southern state—we estimate that we obtained 27 percent of the relevant platforms (160 out of a possible 594, based on the assumption of each state party writing a platform every other year).

75 Matthew Denny and Arthur Spirling, “Text Preprocessing for Unsupervised Learning: Why It Matters, When It Misleads, and What to Do about It,” Political Analysis 26, no. 2 (2017): 168–89.

76 First, we removed nonword character strings (such as numbers and punctuation), converted all letters to lowercase, and stripped out extra white space. In determining the central political issues discussed by the state party platforms, not all of these word stems were equally useful. The “stop words” such as “the” and “too” are sufficiently common that they are likely to be found in many types of speech, and so we removed approximately 100 stop words from the data. We also removed word stems that appeared to be state-specific, either because they were elements of state names (such as “california”) or because they were word stems that some states’ platforms happened to use while others did not (e.g., “pledg”). We then removed any word stems that did not appear at least five times in two separate states.

77 Note that we removed any bigrams that appear in fewer than 0.6 percent of platforms due to sparsity.

78 As a first stage, Coffey, in “State Party Activists,” did use a computer coding drawn on a dictionary of liberal and conservative words, but he then manually went over each coding decision.

79 Kevin M. Quinn, Burt L. Monroe, Michael Colaresi, Michael H. Crespin, and Dragomir R. Radev, “How to Analyze Political Attention with Minimal Assumptions and Costs,” American Journal of Political Science 54, no. 1 (2010): 209–28; Justin Grimmer and Brandon M. Stewart, “Text as Data: The Promise and Pitfalls of Automatic Content Analysis Methods for Political Texts,” Political Analysis 21, no. 3 (2013): 267–97.

80 We dropped trigrams that referred to internal convention procedures (e.g., “state central committee”; “state convent assembl”; “state platform adopt”), that referred to governing bodies with no implication of policy or symbolic content (e.g., “unit_stat_senate; presid_unit_stat), or that appeared to be generic language with no content (e.g., pledg_continu_support). We did include references to specific state agencies (e.g., _state_depart_agricultur) since that could tap into the substantive priorities of the platform, along with references to the Constitution, as that might signal symbolic priorities or orientation. We also include references to multiple governmental layers or bodies (e.g., state_feder_govern) since that might tap into views of federalism. The patterns regarding changing polarization are unaffected by adopting a stricter or looser criterion for inclusion.

81 The gap is simply the difference in the proportion of usage between the two parties (on a per-platform basis).

82 The trigram “innoc_human_life” falls just outside the top twenty and is dominated (100 percent) by Republicans.

83 This analysis was conducted on a slightly large corpus that includes 258 platforms from before 1918.

84 The figures also point to differences in how the two parties talk about the same issue. Consider the abortion-related trigrams in Appendix Figure A.5. While some are used almost entirely by Republicans (e.g., “support human life”) or by Democrats (e.g., “women right choose”), trigrams like “roe_v_wade” have been more balanced, with some over-time shifts.

85 See also Paddock, State & National Parties; Carr et al., “Origins of the Culture War.”

86 The pattern with respect to mentions of rights is slightly more complicated, with Democratic platforms leading an earlier increase in the 1960s and 1970s and Republican platforms leading the increase more recently.

87 See, especially, McCann, Pamela J. Clouser, Shipan, Charles R., and Volden, Craig 2015. “Top-Down Federalism: State Policy Responses to National Government Discussions,” Publius: The Journal of Federalism 45, no. 4 (2015): 495–525CrossRefGoogle Scholar.

88 In a highly nationalized polity, we would expect the state parties to discuss similar issues, irrespective of those issues’ particular relevance for specific states (or the extent of state governmental authority on that issue). Terrorism might occupy the attention of many states, even those that are unlikely targets. In a less nationalized polity, by contrast, states are more likely to focus on distinctive issues: Water conservation, charter schools, or wolf hunting might get top billing in some platforms while being ignored elsewhere. To be sure, truly state-specific issues are disadvantaged by our set-up, in which word stems need to appear in 0.25 percent of all segments to be analyzed. But this threshold is sufficiently permissive that many regional issues should still make the cut, especially if they are a persistent feature of a state's agenda. Additionally, we are interested in the extent to which the state platforms’ topics shift together over time.

89 Blei et al., “Latent Dirichlet Allocation.”

90 See, e.g., Lauderdale, Benjamin E. and Clark, Tom S., “Scaling Politically Meaningful Dimensions Using Texts and Votes,” American Journal of Political Science 58, no. 3 (2014): 754–71CrossRefGoogle Scholar.

91 Chang, Jonathan, Boyd-Graber, Jordan, Gerrish, Sean, Wang, Chong, and Blei, David, “Reading Tea Leaves: How Humans Interpret Topic Models,” Neural Information Processing Systems 32 (2009): 288–96Google Scholar.

92 Lauderdale and Clark, “Scaling Politically Meaningful Dimensions”; Hopkins, The Increasingly United States.

93 Butler and Sutherland, “Have State Policy Agendas Become More Nationalized?”; Das et al., “All (Mayoral) Politics Is Local?”

94 The figures present the results of an initial LDA model fit to the platforms and estimated via variational inference.

95 For an account of the rising importance of subnational labor regulation in recent decades, See Daniel J. Galvin, “The Construction of Subnational Work Regulation,” Industrial and Labor Relations Review (August 2020),

96 Grimmer, Justin and King, Gary, “General Purpose Computer-Assisted Clustering and Conceptualization,” Proceedings of the National Academy of Sciences 108, no. 7 (2011): 2643–50CrossRefGoogle ScholarPubMed; Denny and Spirling, “Text Preprocessing for Unsupervised Learning.”

97 Schickler, Racial Realignment

98 Adams, Greg D., “Abortion: Evidence of an Issue Evolution,” American Journal of Political Science 41, no. 3 (1997): 718–37CrossRefGoogle Scholar; Carr et al., “Origins of the Culture War.”

99 Katherine J. Cramer, The Politics of Resentment: Rural Consciousness in Wisconsin and the Rise of Scott Walker (Chicago: University of Chicago Press, 2016).

100 Gentzkow et al., “Measuring Group Differences.” By contrast, estimates of polarization based on congressional roll call votes suggest a more gradual rise in polarization beginning in the late 1970s, e.g., Keith T. Poole and Howard Rosenthal, Congress: A Political-Economic History of Roll Call Voting (New York: Oxford University Press, 1997); Nolan McCarty, Keith T. Poole, and Howard Rosenthal, Polarized America: The Dance of Ideology and Unequal Riches (Cambridge, MA: MIT Press, 2006).

101 As Appendix Table A.4 shows, the bigrams again return very similar results, with civil rights, education, constitutional rights, and abortion being among the most polarized topics.

102 Gentzkow et al., “Measuring Group Differences.”

103 For similar uses of these measures, see also Butler and Sutherland, “Have State Policy Agendas Become More Nationalized?”; Das et al., “All (Mayoral) Politics Is Local?”

104 Bawn et al., “A Theory of Political Parties.”

105 Butler and Sutherland, “Have State Policy Agendas Become More Nationalized?”; Das et al., “All (Mayoral) Politics Is Local?”

106 Galvin, Presidential Party Building; Rodden, “Geographic Distribution”; Grossman and Hopkins, Asymmetric Politics.

107 Hertel-Fernandez, State Capture.

108 The relatively low estimate for state differences among Democrats in 1990 is likely attributable to the very small sample size of Democratic platforms that year (n = 14). Note that the differences in 1992–96 are much higher than in the second half of the period.

109 But see Rogers, “Electoral Accountability”; Grumbach, “From Backwaters”; Hopkins, The Increasingly United States; Grossmann, Red State Blues; Hertel-Fernandez, State Capture; Caughey and Warshaw, Dynamic Democracy.

110 Gentzkow et al., “Measuring Group Differences.”

111 Bawn et al., “A Theory of Political Parties”; Azari, “Weak Parties, Strong Partisanship”; Rosenfeld and Schlozman, “The Hollow Parties.”

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