Barack Obama is taking a day off from the campaign trail on Thursday, a decision he can apparently afford.

Campaign financing numbers out of the Democratic presidential race are expected to show a widening dollar lead for Obama over Hillary Clinton, and possibly another obstacle to Clinton's effort to stay competitive in the last 10 nominating contests yet to be held.

The Obama campaign announced early Thursday that it had earned $40 million in March. The number doesn't match the record performance of $55 million in February, but is still stellar, with the campaign reporting 218,000 new donors and more than 442,000 total donors in March. To date, Obama has raised money from more than 1.2 million donors.

"Senator Obama has always said that this campaign would rise or fall on the willingness of the American people to become partners in an effort to change our politics and start a new chapter in our history," campaign manager David Plouffe said in a statement.

"Today we're seeing the American people's extraordinary desire to change Washington, as tens of thousands of new contributors joined the more than a million Americans who have already taken ownership of this campaign for change. Many of our contributors are volunteering for the campaign, making our campaign the largest grassroots army in recent political history," Plouffe said.

The Clinton campaign said they earned about $20 million in March, compared to $34.5 million in February. According to campaign financing reports, Obama has earned $195 million from the start of his campaign through February 2008. Clinton has made about $167 million.

We knew that he was going to outraise us," Clinton communications director Howard Wolfson said. "He has outraised us over the last several months."

Tapping donors continues to be a priority for the candidates ahead of the April 22 Pennsylvania primary. Obama has scheduled fundraisers at the homes of four different financial backers Sunday afternoon and evening in northern California.

Clinton too is in California, doing a foursome of fundraisers that started Wednesday night in Silicon Valley. She also was attending events with donors in San Francisco, Pasadena and Los Angeles. They are expected to earn $2,300 per person, the maximum allowed by law.

One of those fundraisers said he feared Clinton's high-dollar donors were tapped too early in the campaign.

"That pool is reduced," Larry Stone, the Santa Clara County assessor and Clinton backer. "Hillary came really late to the game in effective fundraising on the Internet as compared to Barack Obama ... Many of the solid enthusiastic Clinton supporters were maxed out."

The fundraising blitz is critical as the candidates head into the final stretch of contests. The outcome in Pennsylvania will be closely scrutinized for signs of strength and weakness for each candidate. Clinton had been running a wide lead in the Keystone State, but Obama has narrowed it to single digits, in part from an expensive and wide ad campaign.

Scott Rasmussen, head of Rasmussen Reports, which runs daily tracking polls of the race, said Obama's "blue-collar charm offensive," which includes visits to factories, bowling alleys and bars, has been aided by his TV buys.

Obama has "spent an awful lot of money on television advertising and absolutely it's working to some degree," Rasmussen said. "He is making progress, he has tightened the race from 15 points a month ago to five points today."

Rasmussen told FOX News that Obama's target audience in the state has long been one of Clinton's strongest demographic groups.

"When you talk about his blue-collar charm offensive, he is trying to tap into this constituency that has long supported Hillary Clinton. The only primary where he has attracted those blue-collar workers so far was in Wisconsin. If he could do that in Pennsylvania, it could lead to a stunning upset, but right now, Hillary Clinton is still ahead," he said.

Clinton aides said Wednesday that they anticipate Obama will outspend her by 2-to-1 in Pennsylvania. In the first round of campaign ads, Obama spent about $2 million to Clinton's $450,000, according to data compiled by TNS Media Intelligence/Campaign Media Analysis Group, which tracks political ads.

Obama is also already airing ads in Indiana and North Carolina, which won't hold primaries until next month.

On a conference call with reporters, Clinton aides chalked up the narrowing poll numbers in Pennsylvania to Obama's aggressive ad buys. But they said polls have tended to portray races as closer than they really are, citing California and Ohio where late deciders broke Clinton's way and helped pull her to victory.

And Wolfson suddenly put the onus on Obama to win Pennsylvania, given the time and money he's spending there.

"If he can't win there it raises serious questions about his ability to compete in those large states ... and his ability to be a strong contender against John McCain in the fall," he said.

He said the campaign doesn't "expect to match Senator Obama ad for ad."

Clinton entered March with $11.5 million to spend in the primary compared to $30.5 million for Obama. Moreover, Clinton owed $8.7 million to several campaign vendors at the end of February. A spot check by The Associated Press of several vendors found many were paid last month, after the March 4 primaries in Ohio and Texas. The cost of those two contests, together with efforts to reduce campaign debt, have kept fundraising a priority for her campaign.

Though the New York senator trails Obama in delegates needed for the nomination, Clinton advisers and fundraisers said her donors remain enthusiastic.

"A big boon to the fundraising has been these appeals for her to withdraw," said Larry Stone, a Clinton fundraiser in Silicon Valley who also is the Santa Clara County assessor. "It makes supporters angry, especially women."

While the money is financing their own intramural Democratic contest, both Obama and Clinton have begun to target McCain. Democratic party leaders have voiced concern lately that the ongoing Democratic race was leaving McCain unscathed.

Obama and Clinton also want to draw sharp contrasts with McCain to influence polling that weighs the two Democrats' relative strengths against McCain. That is especially important to Clinton, who is trying to sell herself as the most electable candidate to the Democratic superdelegates, the party and elected officials who can support whomever they choose, regardless of the election outcomes in the states.

FOX News' Aaron Bruns and The Associated Press contributed to this report.