Obama's Challenge: Gain Lead in Polls

"Frankly, I'm worried about money," the source said. "With Mitt putting his own money in the race, a bunch of money for us might wind up looking like a pittance by comparison."

[an error occurred while processing this directive]

Thompson's campaign manger, Bill Lacy, said he is not concerned, saying that Thompson needs only "a threshold amount of money" to fund effective campaigns in Iowa, New Hampshire, South Carolina and Florida.

"Our bottom line: We are running what I would call an insurgency-style campaign," Lacy said in an interview. "We will spend a lot less money than Mayor Giuliani or Mitt Romney. I am not of the view that the candidate that spends the most money wins."

Thompson's campaign has started a contest to get small towns to raise money, promising that the town with "most donations per capita" will get a visit from the candidate.

A Giuliani fundraiser who previously raised money for President Bush said he has noticed a dramatic difference in the response he has been getting. While an event might have raised $500,000 or more for George W. Bush in 2000 or 2004, a Giuliani event is more likely to yield $200,000, he said.

"I'm hoping, when you have a Republican nominee, we'll have much more engagement," the Republican fundraiser said.

Sen. John McCain (R-Ariz.) continued to struggle this summer after a devastating second-quarter fundraising collapse. But aides expressed confidence that though McCain's numbers will not compare with his rivals', he will have enough. His campaign is planning a six-state fundraising swing, with a major event scheduled in New York City.

One adviser said that McCain's fundraising has picked up since a well-reviewed debate performance and his decision to launch a "no-surrender" tour in which he argues for continuing the U.S. involvement in Iraq.

"There's no question that, politically, having McCain out there on the issue where he has the most credibility and where he's the most knowledgeable . . . helps the poll numbers, helps the press and, in turn, helps the fundraising," the adviser said.

Staff writers Michael D. Shear and Anne E. Kornblut and washingtonpost.com writer Chris Cillizza contributed to this report.