McCain has had the same problem. Although he appeared to receive more small donations in March, small donors made up 13% of McCain's total as of the end of February -- compared with 26% for Clinton and 41% for Obama, according to the nonpartisan Campaign Finance Institute.
Experts point to a variety of reasons for the GOP's inability to match the Democratic Party's Internet receipts. Democratic donors tend to be younger than Republicans, rely more heavily on the Internet and are accustomed to using credit cards to make purchases online.
Republican donors appear to be less trusting that websites will protect their credit card information, and respond to direct mail appeals by writing checks.
That places the GOP at a disadvantage. The cost of generating e-mails is a fraction of the cost of mass mailings. With credit card transactions, candidates gain almost immediate access to the donation.
"That is the real issue facing the McCain campaign at this point. They're not getting that easy money flowing over the Internet," Corrado said.
Also adding to McCain's problems: Some traditional sources of GOP money are leaning Democratic in this campaign.
Obama has received $6.8 million from the securities and investment industry, compared with McCain's $3 million, according to the nonpartisan Center for Responsive Politics. Clinton has received $5.7 million in real estate industry donations; McCain, $2.5 million.
Some individual donors who raise large sums from their friends remain on the sidelines. Through the end of March, McCain received money from less than one-fourth of Bush's largest fundraisers, dubbed Pioneers and Rangers, a Times analysis shows.
One such bundler is Los Angeles investor Thomas R. Tellefsen. In the Republican primary, Tellefsen was Mitt Romney's largest single fundraiser, helping to rake in millions for the former Massachusetts governor.
Romney himself promises to raise $15 million for McCain, and some of Romney's biggest backers have joined the effort. But not Tellefsen. He said he needed a break from politics after Romney pulled out.
Besides, McCain's campaign hadn't contacted him.
"I have not had any communication," Tellefsen said.
Schmidt said most donors were falling into line. At least 75 Pioneers and Rangers who had been backing other Republicans shifted to McCain in February and March, the Times analysis shows.
