Updated

WASHINGTON -- President Barack Obama, campaigning as if his name were on the ballot, implored voters in Philadelphia stump speech to use the three weeks left in the congressional election campaign to "stay fired up" and go to the polls to prevent a Republican landslide.

The president relied on an oft-used speech as he addressed the crowd in the city's Germantown community with the driving cadences that swept him into the White House two years ago.

He and the Democratic party know, however, that this year finds Democrats imperiled because of what has become known as the "enthusiasm gap," with party voters expected to stay away from the polls in a nationwide vote that was widely expected to hand the majority in the House of Representatives and, perhaps, the Senate to Republicans.

"I think the pundits are wrong. I think we're going to win. But you've got to prove them wrong," Obama said, jabbing his finger toward the audience. "They're counting on you staying home. If that happens they win."

There are ample reasons for Republican optimism. Poll after poll shows deep voter discontent and even anger at Obama's and congressional Democrats' leadership. Obama and his fellow Democrats are being blamed for the slow economic recovery and continuing high unemployment.

On Friday, the Bureau of Labor Statistics -- in the last major economic news before the November elections -- delivered another painful blow to Democrats: The U.S. lost 95,000 jobs in September and unemployment remained stubbornly stuck at 9.6 percent.

In another complication for Democrats, the government is expected to announce this week that more than 58 million Social Security recipients will go through another year without a cost-of-living increase in their monthly benefits.

It would mark only the second year without an increase since automatic adjustments for inflation were adopted in 1975. The first year was this year.

Vice President Joe Biden joined Obama at the rally, where the hip-hop band the Roots warmed up the crowd.

It was the second of four large rallies designed to recapture some of the big-stage excitement that Obama created in 2008 with stirring speeches to thousands of young and first-time voters. The president spoke to more than 17,000 people last week in Madison, Wisconsin, where many more thousands watched on screens in an overflow area. Several thousand turned out in Philadelphia on a beautiful autumn afternoon.

As Obama rallied Democrats, the national party put together a new television ad that accuses the business-friendly U.S. Chamber of Commerce of secretly using foreign money to support Republican candidates in the congressional election, which was already forecast to wipe out the Democratic majority in the House of Representatives.

Key Republican operatives hotly rejected the allegations that echo remarks by President Barack Obama in a speech last week.

Obama and the Democratic apparatus are in all-out campaign mode as they try to limit the damage in the Nov. 2 balloting with voters expected to turn in massive numbers to the Republicans and their ultraconservative tea party allies.

While polling of a generic choice among voters between party candidates shows Democrats slightly narrowing a huge Republican lead, chances appear slim anything can be done in the final three weeks of the campaign to prevent Republicans from taking a majority of seats in the House and, perhaps, the Senate.

Democrats presented no evidence to substantiate the charge against the Chamber of Commerce. The use of foreign funds for U.S. campaign activities is prohibited.

The Democratic National Committee ad calls the chamber "shills for big business" and says it is spending millions from anonymous donors to help Republican candidates.

"It appears they're even taking secret foreign money to influence our elections," the ad says. "It's incredible, Republicans benefiting from secret foreign money."

Appearing on Sunday talk shows, a pair of leading Republican strategists accused Obama and Democrats of lying.

"They have not one shred of evidence to back up that baseless lie," said Karl Rove, who was a top adviser to President George W. Bush.

"Have these people no shame?" Rove said. "Does the president of the United States have such little regard for the office that he holds that he goes out there and makes these kind of baseless charges against his political enemies? This is just beyond the pale. How dare the president do this."

The chamber, one of the nation's most powerful business lobbies, spent more than $10 million in ads last week for candidates in House and Senate races around the country, mostly to help Republicans. That is the biggest one-week expenditure of the campaign so far by anyone but the national political parties. The chamber has not revealed where the money came from and is not required to.

Asked to back up the allegation on one of the Sunday news programs, White House adviser David Axelrod offered no proof but said, "Why not simply disclose where this money is coming from and then all of these questions would be answered."

Axelrod said corporate interests are spending huge sums to help Republicans in the elections, calling those expenditures "a threat to our democracy."

Ed Gillespie, former chairman of the national Republican Party, said Republicans are following the same rules of disclosure that permitted presidential candidate Obama to not specify where all his contributions came from in 2008. He accused the White House of trying to intimidate its political opponents.

"These ads are not a threat to democracy," Gillespie said of the chamber's efforts. "They may be a threat to their power, but their power and democracy are not the same thing, and it's very revealing that they see it that way."

Chamber officials say that out of the chamber's $200 million annual budget, $100,000 comes from American business interests abroad. They say that money is used to help finance the chamber's international programs and doesn't use any of it for U.S. political activities.

Tom Collamore, a senior chamber vice president, said the Democratic were trying to change the subject, calling the ad is "ridiculous and false."