Polls suggest that after Lincoln, the most imperiled Democratic senator is Russ Feingold of Wisconsin. The three-term senator, best known for revising campaign finance laws, was not seen as particularly vulnerable a few months ago.
But Republican challenger Ron Johnson, a political newcomer, turned Feingold's seniority against him in this season of antiestablishment fervor. His well-run campaign, coupled with Wisconsin's sluggish economy, have put Feingold in a hole.
If Democrats are deeply worried about Feingold, Republicans similarly feel that a once-promising chance may be slipping away in West Virginia, for the seat long held by the late Robert Byrd. The Democratic nominee, Gov. Joe Manchin, is popular. His state voted heavily against Obama, however, and the president's approval ratings there remain low.
Republican nominee John Raese has tried to tie Manchin tightly to Obama. But revelations that Raese's wife lives and votes in Florida, plus a GOP TV ad production that sought "hicky" actors to portray West Virginia voters, seem to have taken a toll.
Republican chances are dimmer against veteran senators in California and Washington.
Three-term Sen. Barbara Boxer of California faces Republican former business executive Carly Fiorina, who says Boxer is too liberal and too steeped in Washington for the times.
In Washington state, three-term Sen. Patty Murray is trying to hold off Republican Dino Rossi, a former state senator who made two unsuccessful bids for governor.
GOP officials say their nominees trail in those two states, but an upset is possible.
Regardless how these races turn out, the Senate will see several new members. Republicans expected to win include Boozman of Arkansas, Marco Rubio of Florida, Rand Paul of Kentucky, Jerry Moran of Kansas, John Hoeven of North Dakota, Roy Blunt of Missouri, Rob Portman of Ohio, Kelly Ayotte of New Hampshire, Mike Lee of Utah and Dan Coats of Indiana (who was a senator from 1988 to 1999).
New Democrats are likely to be Chris Coons of Delaware and Richard Blumenthal of Connecticut.
Wins by Buck, Angle, Fiorina or Rossi would expand the freshman class. Illinois, Pennsylvania and West Virginia will send rookies, no matter who wins there.
In Alaska, tea partier Miller seemed poised to join that group after stunning Murkowski in the GOP primary. But a series of gaffes and negative reports about his background sent Miller reeling. Murkowski hopes to become the second person to be elected to the Senate through write-in votes, after Strom Thurmond in 1954.
If Republicans come within a seat of taking the Senate majority, they may spend years second-guessing the Delaware primary. Popular GOP congressman Mike Castle was favored to win Vice President Joe Biden's former Senate seat. But tea party upstart Christine O'Donnell beat him in the Republican primary, only to see her fortunes quickly fall, despite assuring voters she is "not a witch."
Democratic spokesman Eric Schultz said Republicans shouldn't be too cocky.
"Like the weather," he said, "politics can be difficult to predict, and we believe Democrats are going to surprise people on Tuesday."
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