President Obama formally launched his reelection campaign Monday morning — illustrating his eagerness to start raising money for a race that could prove difficult but exposing himself to criticism for focusing on politics despite pressing crises at home and abroad.

The announcement — via an e-mail message and a Web video to supporters — makes Obama the first declared candidate in the 2012 presidential race.

By filing his candidacy papers Monday with the Federal Election Commission, the president will be able to start raising campaign money immediately. He has already tapped a campaign manager, former White House deputy chief of staff Jim Messina, who is setting up the headquarters of Obama’s 2012 operation in Chicago.

But some Republicans are criticizing the president for starting his 2012 campaign while a potential government shutdown looms, unemployment remains near 9 percent and U.S. forces are helping to enforce a no-fly zone and arms embargo in Libya.

The actual declaration was a formality, as Obama was widely expected to seek a second term. But in the message to supporters, the president argues that he needed to start his campaign as quickly as possible. He does not speak in the two-minute video, which shows supporters across the country talking about the importance of gearing up for the campaign.

“We’re doing this now because the politics we believe in does not start with expensive TV ads or extravaganzas, but with you — with people organizing block-by-block, talking to neighbors, co-workers, and friends. And that kind of campaign takes time to build,” Obama wrote in the e-mail message. “So even though I’m focused on the job you elected me to do, and the race may not reach full speed for a year or more, the work of laying the foundation for our campaign must start today.”

Obama’s move comes at a complicated time in his presidency. Statistics released last week show that unemployment has dropped a full percentage point, to 8.8 percent, since the November midterm elections, leading the administration to tout progress on an issue that has dogged the president.

But Democrats and Republicans remain at odds over federal spending, and Obama’s decision to intervene in Libya has not gained majority support from the public.

A recent Washington Post-ABC News poll showed 51 percent of Americans approve of Obama’s performance, while 45 percent disapprove, making him a favorite but far from guaranteed to win reelection, according to strategists in both parties.

The Republican National Committee released a minute-long video Monday in response to Obama’s announcement. It opens with images of the president playing golf, filling out his NCAA bracket and appearing on the television talk show “The View.” Then, it flashes the numbers: 8.8 percent unemployment, nearly 3 million jobs lost.

“You’ve been enjoying yourself. But now it’s time to make them love you again. You’re cool. Calm. Collected. You’ve always gotten what you wanted. But was it ever what we wanted? We need jobs. We need leadership,” the narrator of the ad says.

Dan Schnur, a former adviser to Sen. John McCain (R-Ariz.) who teaches at the University of Southern California, said the benefit for Obama of declaring early “is logistical. When you start raising money in April rather than October, you can raise more money.”

“The potential downside is it’s hard for him to draw a contrast with the opposition and excite Democrats,” Schnur said, “because there is not an alternative on the other side.”

Obama’s formal entrance into the race comes as his potential challengers are playing a surprising waiting game. For the 2008 race, former senator John Edwards (D-N.C.) announced his candidacy in December 2006, and former Massachusetts governor Mitt Romney (R) did the same two months later. The entries of those two prominent candidates effectively forced other contenders to start as well, and almost a dozen candidates, including Obama, were running by April 2007.

This time, although former Minnesota governor Tim Pawlenty (R) formed an exploratory committee last month and is virtually certain to run, as is Romney, none of the most prominent Republicans has made it official.

And Republicans say the first member of their party to enter would face what Obama already has to deal with as president: the pundits, press and their opponents watching their every move.

“The key thing is that you get different scrutiny when you file as candidate,” said Ed Rollins, who managed Ronald Reagan’s 1984 reelection campaign and is a top adviser to potential candidate and former Arkansas governor Mike Huckabee (R). “If you get in first, you get that boost, but you get all of that scrutiny as well. My sense is if one had jumped in early and was viable, others may have jumped in as well. Now, it’s a game of chicken.”

Democrats hope to raise enough money by the start of 2012 to develop the kind of extensive get-out-the-vote operations and television commercials in key states that helped Obama win last time.

Rollins said he is expecting that Obama, whose campaign wants to raise more than the $750 million it did in 2008, will again have more money than his GOP challenger. But he said Republican donors showed in the 2010 congressional elections that they were ready to open their wallets to beat Democrats.

A Republican general-election candidate simply needs enough money to run a credible race, Rollins said; raising more than the incumbent isn’t required.

Obama’s numbers have dipped in key states that he won in 2008, such as Ohio, Pennsylvania and Wisconsin, and will need to win reelection next year. And Democrats say Obama probably cannot win any states in 2012 that he didn’t win in 2008.

At Democratic fundraisers over the past month, Obama has already started laying out the case he will make to the public for a second term: passing major legislation such as last year’s health-care bill, rebuilding the American economy, winding down the war in Iraq. And unlike 2008, he has a few major advantages: 13 million campaign donors who gave him money three years ago, the megaphone of the presidency to draw attention to whatever issue he wants — not to mention Air Force One.

At the same time, unemployment is likely to remain above 7 percent, even by the end of 2012, and Romney and other potential Republican candidates are already blaming Obama for the sluggish economy. Many of his policies, such as the health-care bill and the stimulus package, are strongly opposed by millions of Americans.

And an incumbent president must balance running for office with managing every crisis that happens on his watch, from a domestic oil spill to civil unrest in the Middle East.

“Despite a looming government shutdown, a new military operation in Libya and Tax Day around the corner, President Obama made the decision to focus on kicking off his billion-dollar campaign,” Republican National Committee Chairman Reince Priebus said in a statement Monday.

“As the debt and reckless spending championed by this administration threatens to snuff out the recovery and future job growth, the president’s conscious decision to take a back seat on leadership is downright irresponsible.”