A screen capture image from a video announcement of US President Barack Obama's 2012 re-election campaign that was launched on April 4, 2011.  [Photo/Agencies]

WASHINGTON - President Barack Obama formally launched his re-election campaign Monday, urging supporters to mobilize again to protect the change he's brought over the past two years.

Between now and the November 2012 election, the incumbent Democrat will work to convince a fickle America that he has delivered change, made the right moves and earned the chance to continue the job. He will have to defend policies that have proven divisive, chief among them his sweeping health care overhaul and his efforts to boost the slow-to-rebound economy.

Obama announced his bid just as the White House is in a budget standoff with Congress that could lead to a government shutdown, weeks after the commander in chief directed US military operations to a third major warfront, Libya, and days after the post-recession economy showed more signs of a rebound with a report that the still high unemployment rate had fallen to 8.8 percent.

"We've always known that lasting change wouldn't come quickly or easily. It never does," the Democrat said in an e-mail to more than 13 million supporters announcing his candidacy. "But as my administration and folks across the country fight to protect the progress we've made - and make more - we also need to begin mobilizing for 2012, long before the time comes for me to begin campaigning in earnest."

He told them he was filing the necessary paperwork with the Federal Election Commission, and directed them to his new campaign website where a launch video featured clips from supporters talking about their continued backing of the Democrat.

"I don't agree with Obama on everything but I respect him and I trust him," Ed from North Carolina says, delivering what's certain to become a key part of the president's pitch as he tries to re-energize liberals who have criticized some of his policies and independents who have fled from him in his first term.

Widely expected, the procedural step of launching a campaign was planned to coincide with the second fundraising quarter of the year. Filing paperwork will allow the president to begin raising money in earnest for what allies say could be a record-breaking haul of more than $1 billion for his campaign. That begins this month; he's slated to visit major money venues of Chicago, San Francisco and Los Angeles in the coming weeks.

The campaign is based in Chicago, and many of the same people from his first bid remain involved, including former campaign manager David Plouffe, who now is in the White House, and chief political strategist David Axelrod.

Managing the campaign this time is Jim Messina, who played a senior role in the first bid and in the White House. Messina has spent the past few months touring the country to lay the groundwork with donors in hopes of building a massive fundraising network featuring both large and small contributions. He's asked some 400 donors - called bundlers - to bring in at least $350,000 this year; the re-election website is geared toward raising money from grass-roots backers. Obama raised $750 million for his 2008 campaign.

Obama faces no primary challenger.

On the other side, the race for the Republican presidential nomination is just getting under way; more than a dozen Republicans are considering seeking the chance to challenge Obama in the next election. Only a few have taken the initial steps toward a candidacy, though several more are expected to this month. It's a wide open race with no clear front-runner.

Nevertheless, Obama said he's not taking anything for granted.

"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," he said in the e-mail.

"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 added. He directed them to the new red, white and blue website for what he said was "a campaign that's farther-reaching, more focused, and more innovative than anything we've built before."

The website features Obama's new campaign logo - 2012 with the rising sun in the background, a version of his 2008 campaign logo - and announces that the campaign is kicking off.

The video is a montage of testimonials from a demographically diverse group of backers who intend to stay involved in this campaign.

"It needs to reflect the changes that we've seen in the last two-and-a-half years," says Katherine from Colorado. "Then we had an underdog senator. Nobody thought that he had a chance. And now he's the president."