WASHINGTON (CNN) -- Former Massachusetts Gov. Mitt Romney flexed his political fund-raising muscles Monday by announcing that he had raised more than $20 million in the first three months of 2007, the largest amount declared so far by a candidate for the Republican presidential nomination.

But Romney and all other presidential hopefuls trail Sen. Hillary Rodham Clinton in the "fund-raising primary" as the New York Democrat collected $26 million in contributions to add to an additional $10 million she transferred from a Senate account to her presidential committee, her committee reported.

Clinton's fund-raising prowess can be attributed to a fine-tuned political machine and national fund-raising network honed during her husband's years in the White House and broadened during her first term in the Senate.

On the Democratic side, according to their campaigns, former North Carolina Sen. John Edwards raised $14 million; New Mexico Gov. Bill Richardson raised $6 million; Connecticut Sen. Chris Dodd raised $4 million; and Sen. Joe Biden, raised between $1 million and $2 million.

For the Republicans, former New York City Mayor Rudy Giuliani raised $14 million; Sen. John McCain has raised $12.5 million; Sen. Sam Brownback has raised $1.3 million; and former Arkansas Gov. Mike Huckabee raised $500,000, according to their campaigns.

The initial fund-raising deadlines are generally considered to be an early indicator of a candidate's viability. But given the fund-raising options available to the candidates -- such as raising money for both the primary and general elections -- it is difficult to compare these figures until the campaigns file detailed financial reports to the Federal Election Commission. The campaigns have released rough estimates of their fundraising, but the complete reports are not due until April 15.

-- CNN Political Unit's Mark Preston and Robert Yoon