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The Democratic National Committee announced this weekend it is pouring money into get-out-the-vote operations in key states, including nearly $1 million in Mr. Obama’s home state of Illinois and $470,000 in Florida.

In a troubling sign for Democrats, they are putting $100,000 into Massachusetts, where a Republican challenger is giving Gov. Deval Patrick a competitive race, and where some of the state’s 10 House seats — currently all held by Democrats — could be won by Republicans.

Candidates across the country canvassed their states and districts, seeking last-minute undecided voters’ support and touting local newspapers’ endorsements.

But in many cases, voters have already made their choices, thanks to early and absentee voting.

In North Carolina, where a few early voters reported trying to vote for a straight Republican ticket but instead the electronic machines spit out a straight-ticket Democratic vote, a federal judge intervened.

Judge Malcolm Howard on Saturday ordered that state election officials post signs warning that the machines are sensitive and cautioning voters to review their ballots carefully before finalizing their votes.

Democrats say they’re banking on independent and undecided voters taking a harder look at Republicans and rejecting the GOP’s policy offerings late in the game.

That explains in part Democrats’ focus on Republicans such as Ms. O’Donnell in Delaware, whose selection by primary voters over Rep. Michael N. Castle has turned what was expected to be a Republican pickup into a near-certain Democratic hold.

Mrs. Palin, who helped boost Ms. O’Donnell in the primary, defended that decision Sunday, arguing that she had to “give it the old college try and allow the conservative in the race” to be heard.

Adding to the circus atmosphere of the final weekend, two television comics, Jon Stewart and Stephen Colbert, held a “Rally to Restore Sanity,” attracting tens of thousands of people to the Mall in Washington.

The irreverent crowd seemed less about politics than about lashing out at the establishment politicians and press who feed on political controversy.

“We hear every damn day about how fragile our country is, on the brink of catastrophe, torn by polarizing hate and how it’s a shame that we can’t work together to get things done, but the truth is we do. We work together to get things done every damn day. The only place we don’t is here,” Mr. Stewart said, pointing at the Capitol behind him, “or on cable TV. But Americans don’t live here or on cable TV.”

Still, the rally’s anti-politics theme didn’t stop Democrats from reportedly trying to recruit volunteers for a late-campaign get-out-the-vote push.

The election is now down to a turnout game.

“Most voters have picked sides. Convincing the few remaining undecided voters is taking a back seat to mobilizing supporters,” said Lee M. Miringoff, director of the Marist College Institute for Public Opinion, which released a final batch of Senate polls this weekend showing tight races in Colorado and Washington, while Republicans held 7-percentage-point leads in Pennsylvania and Wisconsin.