Obama's Challenge: Gain Lead in Polls

"The third is tougher on everybody," said Jim Dyke, a senior consultant to former New York mayor Rudolph W. Giuliani (R), referring to the third quarter. "There has been such a massive infusion already. The system has been squeezed so hard already."

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Or as Kevin Madden, spokesman for former Massachusetts governor Mitt Romney (R), put it: "Look, the whole country was on vacation. It's a tough quarter."

Through June, the candidates combined had raised $276.6 million, almost three times what earlier contenders had raised at the end of the second quarter in 1999 and in 2003, for the presidential races in 2000 and in 2004.

The early crush to raise money also means that many potential donors have already reached the legal limit of their giving: $2,300 per person. So far, 70 percent of Clinton donors have "maxed out," forcing Clinton, who had raised $52.5 million for the primaries by the end of June, to look for new contributors.

"Presumably, the low-hanging fruit was plucked at the beginning," said Jan Baran, a campaign finance lawyer. "Her campaign, like most campaigns, are going to find it increasingly difficult to locate new donors."

Aides to Edwards, who has struggled to keep pace with Clinton and Obama both in the polls and in fundraising, said they are on track to meeting their goal of raising $40 million by the time the primary voting begins.

"We're on track with our four-state, $40 million strategy, which is the amount our campaign believes will be enough to aggressively get our message out in each of the early states," spokeswoman Colleen Murray said.

Among Republicans, Romney is leading in Iowa and New Hampshire polls but lags far behind in national surveys, struggling to break into double digits in most of them. Aides are working overtime to keep expectations low.

"The campaign remains focused on building our grass-roots fundraising infrastructure with help from volunteer donors and supporters," Madden said.

Romney has already tapped his vast personal wealth in the first half of the year, contributing $9 million to the campaign. It has been reported that he is willing to put a total of $80 million into the campaign. Still, Romney has several fundraisers scheduled, including at least a half-dozen in California. His supporters are also being pushed to host their own mini "rallies" in cities across the country, each with a goal of raising $1,000 for the campaign.

Other Republicans are also working hard to tamp down expectations.

A source familiar with the fundraising efforts of former senator Fred D. Thompson (Tenn.) said that, while the newest addition to the Republican field is "hitting his targets," there is concern that the amount could appear small when stacked next to his rivals'. Thompson's first report showed that he raised about $3 million in June.