President Obama flexed his campaign muscle a day after Republicans came closer to selecting a challenger, jetting back to his home town for a surprise visit to his 2012 election headquarters and rallying supporters at three fundraisers.

Less than 24 hours after former Massachusetts governor Mitt Romney emerged as the clear front-runner for the GOP nomination by winning the New Hampshire primary, Obama paid his first visit to his reelection headquarters, in a 50,000-square-foot office in the Prudential Building here. The stop was not announced ahead of time to reporters traveling on Air Force One, and they were not allowed inside.

Later, White House aides said that Obama spoke in an open, bullpen-style area on the sixth floor, reminiscing about his arrival in Chicago as a young man and his Senate campaign in 2003.

The president thanked staffers and encouraged them to run “a campaign that embodies the values we’re fighting for,” deputy press secretary Josh Earnest quoted him as saying.

A short time later, Obama rallied 500 supporters at the University of Illinois-Chicago, playing off his 2008 slogan, “Change you can believe in.”

“Change is hard, but it is possible,” Obama said after listing such accomplishments as ending the Iraq war, rescuing the auto industry and passing health-reform legislation.

“I’ve seen it, you’ve seen it, we have lived it,” he added. “And if you want to end the cynicism and end the game-playing that passes for politics these days and you want to send a message about what is possible, you can’t back down. Not now. You can’t give up. Not now. You have to keep pushing and fighting for the change we can believe in.”

Aides have said that Obama is focused on governing, not campaigning, but he has held five fundraisers this week alone.

Before heading to Chicago, the president had gathered business leaders to talk about how to create jobs at home. Although officials said the event was not political, it implicitly contrasted the president’s jobs push with Romney’s record at Bain Capital. Romney has been attacked by rivals for Bain's tactics of restructuring companies and sending jobs abroad.

In Chicago, Obama cited his meeting with the CEOs and told the crowd that Republicans favor policies promoting “on-your-own economics.”

Of his own record, Obama said: “I’m not a perfect man. I’m not a perfect president, but I’ve kept this promise: I’ll always tell you what I believe in. I’ll always tell you where I stand. So if you’ve still got that energy, if you’re still fired up . . . if you want to keep reaching for that vision you hold in your hearts, I promise you, change will come.”