How do white evangelicals, as a small minority group, exert such outsized control on American politics at a national level (I'm piggybacking on my previous posting with this question)? As Jacob Lupfer explains, it's by monitoring the boundaries of political and religious conversations, and excluding anyone who will not dance to their right-wing tune — including potential candidates for national office:
Obama is a liberal Protestant. Evangelical leaders loathe liberal Protestants, and many consider them modern-day heretics. In fact, evangelicalism emerged largely as a reaction against liberal Protestantism. In many ways, mainline Protestantism is a foe that evangelicals have largely vanquished in our time, so the persistence of Christians such as Obama and Hillary Clinton in positions of power and influence is maddening to conservative evangelicals who feed on a narrative of their own ascendancy and mainline decline.
Boundary maintenance is very important to white evangelicals; they like to be clear about who is in and who is out. Given the rapid acceptance of homosexuality and same-sex marriage, even in some evangelical circles, leaders are especially preoccupied with their gatekeeping role.
And, of course, the tribalistic dynamic that Lupfer is describing (and accurately so) among white evangelicals is also richly represented in the right wing of American Catholicism, which is closely allied with (and theologically indebted to) right-wing white evangelicalism. If you're not persuaded I'm right about this, just read the comments at any Catholic blog site these days, including ones that purport to represent some kind of mythic "center" that transcends the divisions of left and right.