The infrequency of issue voting in American presidential elections is usually attributed to a lack of policy rationality among voters. An examination of the Vietnam war issue in 1968 suggests, however, that much of the explanation may lie instead with the electoral process itself, and with the kinds of choices which are offered to citizens.
Policy preferences concerning Vietnam were only weakly related to the two-party vote. Less than 2 per cent of the variance in voting choices between Nixon and Humphrey could be accounted for by opinions on Vietnam. Yet the absence of issue voting could not be fully explained by voters' failings. Most people had strong opinions about Vietnam. The public was generally able to perceive where prenomination candidates stood on the issue. People were able and willing to take account of Vietnam in evaluating other candidates.
Voters did not bring their Vietnam preferences to bear upon the choice between Nixon and Humphrey because they saw little difference between the positions of the two, and because they were not certain precisely where either one stood. These perceptions, in turn, were rooted in reality. Humphrey's and Nixon's campaign speeches show that they did differ rather little on specific proposals about Vietnam. Further, both candidates indulged in so much ambiguity about Vietnam that public confusion over their positions was understandable.
There are theoretical reasons for believing that candidates in a two-party system often have an incentive to converge at similar policy positions, and to be vague. If they generally do so, their behavior may contribute significantly to the apparent nonrationality of voters. In addition, it may have important implications for questions of collective rationality and social choice.