The chart that I’m going to show you is one of the more important ones that we’ve presented at FiveThirtyEight in some time. It helps explain a lot of what’s going on in American politics today, from the negotiations over the federal debt ceiling to the Republican presidential primaries. And it’s pretty simple, really, although it took me some time to track down the data.
Here’s what the chart will show: The Republican Party is dependent, to an extent unprecedented in recent political history, on a single ideological group. That group, of course, is conservatives. It isn’t a bad thing to be in favor with conservatives: by some definitions they make up about 40 percent of voters. But the terms ‘Republican’ and ‘conservative’ are growing closer and closer to being synonyms; fewer and fewer nonconservatives vote Republican, and fewer and fewer Republican voters are not conservative.
The chart, culled from exit poll data, shows the ideological disposition of those people who voted Republican for the House of Representatives in the elections of 1984 through 2010. Until fairly recently, about half of the people who voted Republican for Congress (not all of whom are registered Republicans) identified themselves as conservative, and the other half as moderate or, less commonly, liberal. But lately the ratio has been skewing: in last year’s elections, 67 percent of those who voted Republican said they were conservative, up from 58 percent two years earlier and 48 percent ten years ago.
This might seem counterintuitive. Didn’t the Republicans win a sweeping victory last year? They did, but it had mostly to do with changes in turnout. Whereas in 2008, conservatives made up 34 percent of those who cast ballots, that number shot up to 42 percent last year. Moderates, on the other hand, made up just 38 percent of those who voted in 2010, down from 44 percent in 2008 (the percentage of liberals was barely changed). The 2010 election was the first since exit polls began in 1976 in which a plurality of the voters said they were conservatives rather than moderates.
http://fivethirtyeight.blogs.nytimes.com/2011/07/07/why-the-g-o-p-cannot-compromise/Here's the OTHER chart:
While self-identified liberals are a growing proportion of Democratic voters, the largest share is (and has been for a considerable period) moderates. We've pushed out most of the conservatives, but some people seem to want to, in the name of ideological purity, have the moderate voters follow them out the door, rather than build a center-LEFT coalition.