Polarizing the U.S. Senate. - Why the Senate historically is ideologically more moderate & bipartisan. Is this on the wane?

From The Washington Post, 01-09-05:

Redder Reds, Bluer Blues Tilting the Senate

The Senate historically has been known for ideological moderation and bipartisanship, but in recent years those traits have been at a premium. An examination of election returns suggests one reason why: The voters electing the senators are themselves growing more partisan.

After last fall's election, there are just 25 senators who come from states that voted for the opposing party's presidential nominee. Sixteen Democrats come from states that went for President Bush, and nine Republicans come from states won by Democratic nominee John F. Kerry.

The 25 are four fewer than were in the Senate after the 2002 election, less than half as many as when Bush's father was in the White House, and the lowest number in at least a quarter-century, according to a Washington Post analysis.

Although perhaps a bit arcane, the data tell an unmistakable story about the rise of partisanship in the electorate. In 1987, for instance, there were 56 senators -- more than half the Senate -- who came from states that voted for a presidential nominee of the opposing party.

Political analysts say the drop is significant because it reveals how most states now have a partisan tilt, with one party clearly in the stronger position up and down the ticket. That means individual senators have less reason to worry about courting voters from the other party, and less incentive to capture the ideological center.

"The trajectory of this is clear," said Thomas E. Mann, a political scientist at the Brookings Institution. "You don't get as much of a difference between presidential voting and voting at other levels. . . . To the extent that members come from states that tend to be strongly red or blue states, it reinforces their preexisting views and tends to work against any kind of accommodation between the parties."

It also tends to diminish the number of moderates. The chamber's leading centrists in recent years -- lawmakers such as just retired John Breaux (D-La.) and Sen. Olympia J. Snowe (R-Maine) -- represented states that often voted one way for the Senate and another for president.

The correlation is not perfect. Sen. Rick Santorum (R-Pa.), whose state has voted Democratic in the past four presidential elections, is considered one of the most conservative senators. But in general, experts said, lawmakers who come from such states must often think twice about how their constituents would react before hewing to a party line on legislation.

The data suggest that some of the same trends influencing political behavior in the Senate are affecting the always-more-partisan House as well, an ominous sign for policymakers hoping to strike bipartisan deals this year on contentious issues such as restructuring Social Security.

While the number has bounced up and down over the years, the long-term trend toward greater partisan alignment in the Senate and in presidential elections is clear. In 1979, there were 40 senators from a party different from that of the presidential nominee who carried his or her state.

The number rose into the 50s after the midterm election in 1986 and stayed there for the remainder of Ronald Reagan's and George H.W. Bush's terms. Then it plummeted from 54 to 33 after Bill Clinton's election in 1992. For the balance of the 1990s, the number of senators from crossover states remained in the 30s.