Obama's presentation in Copenhagen on Friday will be the first time a U.S. president has appeared before the International Olympic Committee to lobby for an Olympics. Obama initially had said he couldn't make the trip because he needed to tend to the health care debate at home.
As the White House announced the change of heart on Monday, there seemed to be increasing confidence that the votes could be stacking up Chicago's way to host the 2016 Summer Games. If Chicago does come away the victor in the four-way race - Madrid, Rio de Janeiro and Tokyo are the other contenders - Obama could get a political boost for helping to deliver the Games to his adopted hometown and for handing the U.S. a fresh source of national pride.
If the U.S. loses, he still might get points for trying. But he would be visibly tied to a failed effort - and to the spending of political capital on an endeavor many Americans might consider unworthy of so much of a president's time and energy.
This is something Obama can ill afford when the public already shows signs of fatigue with his major efforts on so many fronts at once, many so far unfulfilled.
"If you actually go to Copenhagen and meet with the Olympic committee, you're really on the line to deliver," said Darrell West, a political analyst at the Washington-based Brookings Institution.
The president already has a lot on the line.
He's re-examining his administration's strategy in Afghanistan, managing the shaky U.S. economy and pushing hard for health care overhaul.
Aides say Obama didn't make the decision to travel until this past weekend, after he returned home from the G-20 economic summit in Pittsburgh and consulted with first lady Michelle Obama and senior adviser Valerie Jarrett. They both were already planning to travel to Copenhagen as the U.S. delegation leaders, due to depart Tuesday.
The president decided that the contentious health care negotiations were "in a better place," making the trip possible, White House press secretary Robert Gibbs said.
The administration was given no advance hint of victory that would make the president's decision less risky, Gibbs said.
Obama's itinerary, allowing him only a few hours in Copenhagen, suggests he is aware he is walking a thin line. The president is flying overnight Thursday, making a presentation to the IOC members on Friday, and returning to Washington the same day. He may not even stick around to see the winning city announced.
Speaking to reporters at The White House Monday, the first lady said she knows his involvement raises expectations for Chicago's bid.
"You're darned if you do, and you're darned if you don't," she said. "I'd rather be on the side of doing it."
She will spend Wednesday and Thursday meeting individual IOC members, then she and the president will each make a presentation during Friday's meeting and take questions from the committee. Mrs. Obama said she's taking with her a lesson learned on the campaign trail.
"One conversation or one example or illustration that connects could make the difference," she said.
The president has long been a supporter of Chicago's bid, and recently sent letters to IOC members promising a "spectacular Olympic experience for one and all."
Heads of state have been instrumental in recent votes, creating somewhat of a new precedent.
Tony Blair helped London win the 2012 Olympics by traveling to Singapore to meet with IOC members ahead of that vote, and Russia's Vladimir Putin went to Guatemala to lobby in support of Sochi's bid for the 2014 Winter Games.
Brazilian President Luiz Inacio Lula da Silva will be in Copenhagen to make the case for Rio. King Juan Carlos of Spain and Spanish Prime Minister Jose Luis Rodriguez will be there boosting Madrid.
IOC executive board member Gerhard Heiberg, who will cast a vote Friday, said Obama's appearance is a positive development for the U.S. "He is a powerful person and a great personality," Heiberg said. "It will make an impact."
And Karl Christian Koch, secretary general of Denmark's Olympic committee, said Obama's trip increases Chicago's chances.
America's supporters in Copenhagen were already high-wattage. The contingent assembled by Chicago's host committee includes talk show host Oprah Winfrey as well as 14 Olympic and two Paralympic gold medalists.
In addition to the first lady and senior adviser Jarrett, the official delegation includes Education Secretary Arne Duncan and Transportation Secretary Ray LaHood. All are from Illinois.
--- Associated Press Writers Nancy Armour in Copenhagen and Graham Dunbar in Geneva contributed to this report.