Partisan polarization has now been on the rise for several decades, and it has become a fact of life in twenty-first-century U.S. politics. At the elite level, the overwhelming evidence presented in this volume (and elsewhere) demonstrates clearly that our two major parties are ideologically as far apart as at any point in our natione's recent history. And at the mass level, while there are strong disagreements regarding the extent to which citizens are ideologically polarized along partisan lines and on a host of issues, it seems abundantly clear that the choices offered to them and the institutions (electoral, legislative, and others) in which social choices are made help to sustain – or at least fail to curb – partisan polarization.

That much seems fairly clear. When we commissioned the papers that form the basis for this volumee's chapters, we asked contributors to examine polarization among voters and activists, among the states, in various federal institutions, and in the media. Our goal was to bring together all these disparate strands into a single volume that would provide the most up-to-date political science scholarship on this very important question. We now have in a single volume the state-of-the-art in the literature on polarization.

What can we conclude on the basis of this extensive research? While the bulk of the literature agrees that polarization is an illness that plagues our current political system (though there are exceptions – as will be shown shortly), some of the chapters in our volume raise serious questions about whether polarization is always deleterious and whether some of the cures may be worse than the disease. To be sure, the vast majority of contributors are of the opinion that polarization hurts the operation of our democracy.

But as scholarship on this topic moves forward, we believe that the debate would benefit from more theoretical and normative discussions about the costs and benefits of partisan polarization as well as a more thorough examination of the conditions under which polarization hurts various constituencies and, conversely, the conditions under which some groups may actually benefit from polarization and, its offshoot, gridlock. If polarization is here to stay – and most contributors to this volume seem to think it is – then we must think of possible solutions.

Partisan polarization among the public, activists, and elected officials characterizes American politics in the twenty-first century, and it is often seen as the major source of our governing problems (Schaffner 2011, Persily 2015). Republicans and Democrats are further apart ideologically than at any point in recent history, expressing highly negative views of the opposing party (Doherty 2014). The deleterious impact of partisan polarization cannot be exaggerated. It discourages compromise, produces gridlock, fosters mistrust, and ultimately hinders the functioning of governmental institutions. Lawmaking, representing, overseeing, executing laws, and adjudicating legal and constitutional disputes requires that individuals who might otherwise disagree come together and serve interests that go beyond their own. Failure to compromise results in gridlock, dysfunction, and partisan warfare. To paraphrase former House Speaker Sam Rayburn, we are not going along, let alone getting along!

It was not always thus. In fact, during much of the twentieth century, our national parties did not exhibit this sort of intense partisan polarization that we have seen emerge over the last generation or so. To understand how we got to where we are today, we must account for the rapid partisan change that the U.S. South has witnessed over the latter half of the twentieth century. Long gone are the days of the conservative southern Democrats (Dixiecrats) holding a more liberal northern caucus in check. Largely as a response to federal intervention in the civil rights arena, conservative southern Democratic voters started to migrate toward the GOP in the mid-1960s. Todaye's southern conservatives are well ensconced within the Republican Party. Southern Democrats in 2014 are largely liberal and nonwhite. The South has realigned politically. A similar, if not somewhat less acute, change occurred in reverse in other parts of the country such as the northeastern and the far west of the United States. With large swaths of the country realigning into one or the other party, each partye's coalition has become much more homogeneous ideologically and in terms of policy preferences. To be liberal in 2014 is to be a Democrat; the same goes for conservatives and Republicans. Battles over the scope and size of the federal government have produced a wide policy schism between parties.

WHY WRITE THIS BOOK?

Although it is true that the literature on gridlock and polarization is extensive, it is also the case that it is quite disparate.