The generation one comes of age politically is an important determinant in one’s political identity. Though a political generation gap is not a perpetual feature of the American political landscape, one’s generation can be a noteworthy influence on partisan and ideological leanings. The political environment experienced by successive generations as they have come of age politically influences political attitudes throughout one’s life. The result is that different generations have distinct political leanings that they will maintain over their lifetimes. Utilizing data collected by the American National Election Studies (ANES) from 1952 to 2016, this study utilizes cohort analysis to compare differences in generational presidential vote choice and ideological preferences over time. The findings suggest that the generational divide in American politics today is unprecedented. For the second half of the twentieth century there was remarkably modest political disparity between generational cohorts. This lack of an age divide in American politics lead the field of political science to generally focus on other demographic gaps in American politics other than generational differences. Once the Millennial Generation first entered the electorate in the early 2000s, however, there has emerged a considerable generational gap in American politics. The Millennial Generation has developed distinct political leanings that are significantly to the left of older generations. Although there is a stereotype that younger Americans are more liberal and supportive of Democrats than older Americans are, from 1952 to 2000 this generally was not the case. In fact, prior to the Millennials, there tended to be little difference between the generations in presidential vote choice and ideological leanings, and the youngest generation was not consistently the most Democratic leaning or liberal. Given Millennials’ left-leaning politics, generational replacement would probably have an important influence of American politics regardless of whomever these voters were replacing in the electorate. The Silent Generation that is currently being replaced in the electorate, however, has in recent years emerged as considerably the most Republican and conservative generation in contemporary American politics. Conservative and Republican-leaning Americans are thus currently being replaced in the electorate by relatively liberal and Democratic-leaning voters. The Millennial Generation thus has the potential to alter the course of American politics.