The Washington Post's Rachel Weiner had a nice story on Sunday about liberal and progressive candidates losing to more moderate and conservative candidates in Democratic primaries. "Three of the seven candidates endorsed by the Progressive Change Campaign Committee, a leading liberal campaign organization, have lost their primaries," she notes. Jonathan Bernstein, a political scientist/blogger, argues that "there seems to be a difference" between Republicans and the Democrats on this score, with moderates more likely to win Democratic primaries than Republican ones. He wonders why this is.
There's an answer! As Bernstein no doubt knows, the GOP is more ideologically unified than the Democratic party. Self-identified conservatives make up a much larger portion (71 percent, as of 2011) of the Republican party than self-identified liberals make up of the Democratic coalition (39 percent as of 2011—up from just 29 percent in 2000). Here are two charts from Gallup that make this clear:
There are some nuances to consider involving the words "progressive" and "liberal." But it's hard to dismiss these numbers.