Including travel, Obama will invest about 7 1/2 hours of his busy day away from the White House, signaling the do-or-die campaign he is leading against a predicted Republican landslide that also could cost Democrats their majority in the Senate.

With the economy struggling to recover from the worst economic downturn since the 1930s Great Depression, unemployment stuck near 10 percent and millions of Americans having lost their homes to mortgage foreclosures Democrats are facing a potentially catastrophic reversal of political fortunes.

A Republican takeover in even one congressional chamber stands to crush Obama’s agenda for the last two years of his presidency and would represent an overwhelming embarrassment for Democrats who broadly increased their power in Washington on Obama’s presidential coat tails just two years ago.

On Sunday, Obama was in Philadelphia campaigning as if his name were on the ballot. He implored voters in a rousing stump speech to use the three weeks left in the campaign to “stay fired up” and go to the polls to prevent a Republican landslide.

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 US 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 recipients in the government’s Social Security pension program would 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 event, 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 US 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 Obama in a speech last week.

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