WASHINGTON  (CNN) -- Sen. Barack Obama raised more than $40 million from more than 442,000 donors in March, his presidential campaign announced Thursday.



Sen. Barack Obama greets campaign volunteers during a stop in Philadelphia, Pennsylvania, Wednesday.



More than 218,000 of the donors were giving for the first time, the campaign said.



The figures are estimates, a campaign spokesman said. "We're still calculating."



Sources in Sen. Hillary Clinton's campaign said the New York senator raised $20 million in March.



Impressive as the $40 million figure is, it is well below the $55 million Obama raised in February. Clinton, Obama's rival for the Democratic nomination, raised about $35 million in February.



Political analysts say this kind of fundraising power catches the attention of voters.



"They add to the so-called 'bandwagon effect' -- the sense that Obama is building, that he's going to be the nominee," said Stu Rothenberg of the Rothenberg Political Report.



With its March totals, the Obama campaign has raised approximately $234 million, which surpasses the Democratic record of $215 million that 2004 nominee Sen. John Kerry raised in that presidential primary season.



Obama is $25 million shy of President Bush's presidential primary fundraising record of $259 million, set in his uncontested campaign in 2004.



Obama raised $194 million through the end of February. Official fundraising tallies for March are due to the Federal Election Commission by April 20.



Clinton raised $156 million through the end of February.



The Clinton campaign said Thursday morning it would not release March figures until required to file its FEC report, two days before the critical Pennsylvania primary April 22.



But later, campaign sources provided the figures, which show March to be Clinton's second-highest fund-raising month for the campaign.



A Clinton spokesman downplayed the importance of Obama's fundraising total.



"We knew that he was going to out-raise us. He has out-raised us for the last several months," Howard Wolfson said after Obama's figures were released. "We will have the resources that we need to compete and be successful in the upcoming primary states."



Wolfson also said he expected Clinton's tax returns to be released soon.



Clinton pledged March 25 she would release her returns within a week.



Sen. John McCain, the expected Republican nominee, raised $11 million in February. He has not announced his March total. E-mail to a friend



CNN's Rebecca Sinderbrand and Rob Yoon contributed to this report.
Who said tax returns will be released soon? Who contributes to Sen. Barack Obama's campaign? Who raised $20 million in March? What did more than 442,000 donors contribute to? When will Clinton release her tax returns?
Wolfson 442,000 donors Sen. Hillary Clinton's Sen. Barack Obama within a week.
question: Who said tax returns will be released soon?, answer: Wolfson | question: Who contributes to Sen. Barack Obama's campaign?, answer: 442,000 donors | question: Who raised $20 million in March?, answer: Sen. Hillary Clinton's | question: What did more than 442,000 donors contribute to?, answer: Sen. Barack Obama | question: When will Clinton release her tax returns?, answer: within a week.