Recent primary results have increased what some talking heads call "polarization." It is less polarization than clarification of political parties. The Democratic Party is more progressive, and the Republican Party is more conservative. That has been true for more than a century. But there used to be a great deal of overlap. Southern Democrats were conservative, all on race and most on other matters. Thre were progressive Republicans -- not all named La Follett.
The clarification continues, Specter and (even if she ekes out a victory in the runoff) Blanche Lincoln combined are a significant percentage of the right wing of the Democratic Party in the Senate.
The Republican results seem to be more the far right defeating the right. Rand Paul defeated Mitch McConnel's preferred candidate in Kentucky. Bennet was not only to the right of the Senate, he was to the right of his party in the Senate. Crist was a moderate, but he would have been a conservative Republican in Eisenhower's day.
The future, and predicitons are hard, especially about the future, looks something like a center-left Democratic Party and a far-right Republican Party.
Poor Arlen Specter couldn't find any place in the new political landscape. He was too Republican for Democratic voters, and not Republican enough for Republican funders.
The history of clarification is long. All Blacks used to be Republican; that changed during the New Deal. Then, in the convention of 1948, Hubert Humphrey pushed through a plank supporting desegregation.
The next steps were Republican. Both Goldwater and Nixon courted Southern segregagionists. That resulted in a brief Republican dominance, holding much of the old base and also much of the "solid south." That eroded rapidly. By W's term, he carried only a few states that had gone for Lincoln. (Goldwater and McCain carried none.)
DeLay changed two things.
- His gerrymandering of Texas got rid of a good many conservative Democrats and converted one into a Republican.
- His habit of ignoring the desires of moderate Republicans persuaded many voters in '06 and '08 to discard them in favor of Democrats.
I don't know how many Congressmen today are between the most liberal Republican and the most conservative Democrat in the House, and with "just say no" it's hard to tell from recent votes. The number, however, is clearly dropping.