First, the electorate has polarized. Over the past two decades, the public’s ideological self-description has changed significantly. In 1992, when Bill Clinton campaigned for president as a reform-minded New Democrat, fully 43 percent of adults thought of themselves as moderate, compared to 36 percent conservative and 17 percent liberal. As the 2012 election got underway, the picture looked quite different. Moderates had declined by 8 points, to 35 percent, while conservatives and liberals had each gained 4 points, to 40 and 21 percent respectively. …

Second, the parties have sorted themselves out along ideological lines. Since 2000, the share of Republicans calling themselves moderate or liberal has fallen from 37 to 27 percent, while the conservative share of Democrats has fallen from 25 to 20 percent. Republicans are more conservative than they used to be, and Democrats are more liberal. Conservatives have increased their share of the Republican Party by 9 points; liberals have increased their Democratic share by 10 points. …

These numbers don’t tell the whole story, however. There’s another key development: above and beyond their ideological disagreements, conservatives and liberals have come to understand the practice of politics differently. In a survey taken right after the Republican sweep in the 2010 midterm elections, 47 percent of American said that it was more important to compromise in order to get things done, versus 27 percent who thought it was more important for leaders to stick to their beliefs even if little got done. Liberal Democrats weighed in on the side of compromise, 58 to 16, moderate Democrats by 64 to 17. But conservative Republicans (the overwhelming majority of their party) favored sticking to their beliefs by 45 to 26. Ten months later, after the debt ceiling fiasco, an outright majority of adults favored compromise, including 62 percent of Democrats and 63 percent of liberals. But pluralities of Republicans and conservatives continued to favor leaders who stuck to their beliefs.