The White House announced Monday that Obama would arrive in Copenhagen on Friday, just before Chicago makes its formal presentation to Olympics officials who are also considering Tokyo, Madrid and Rio de Janeiro. A decision is expected later that day, within hours of Obama's appearance.
No previous U.S. president has made such a trip on behalf of a city vying to host the Olympics.
The visit is a gamble for Obama. He will be leaving Washington with thorny foreign and domestic issues unresolved, and risks looking diminished if Chicago's bid falls short.
The converse is also true: a Chicago victory would be a feel-good moment for both a nation and a president wrestling with crises in Iran and Afghanistan and partisan wrangling at home.
As his proposed healthcare overhaul struggled to gain traction in Congress, Obama had talked about skipping the trip and relying instead on First Lady Michelle Obama as Chicago's A-list advocate. "I would make the case in Copenhagen personally if I weren't so firmly committed to making real the promise of quality, affordable healthcare for every American," the president said on Sept. 16.
But White House aides said that Obama always wanted to make the trip and that he now thought he could dash to Denmark without being diverted from a crowded agenda.
"I believe he felt strongly and personally that he should go and make the case of the United States, and that's what he's going to do," White House Press Secretary Robert Gibbs said Monday.
The announcement is a clear boost for Chicago, where the first family still owns a home within walking distance of the proposed Olympic stadium. Mayor Richard M. Daley is also sending a team of celebrities -- including talk show host Oprah Winfrey and former Olympians -- in support of the bid.
By simply attending the meeting, Obama gives the impression of federal support for the Games, even though the U.S. will not guarantee losses if they occur.
Other foreign leaders have made similar last-minute personal appeals on behalf of their countries in recent years. Tony Blair, British prime minister at the time, was credited with helping London win the 2012 Summer Games, and Russian leader Vladimir Putin helped seal the 2014 Winter Games for Sochi.
Obama plans to be in Denmark only four or five hours, just long enough to see Chicago's presentation, participate in the subsequent question-and-answer session and mingle briefly with Olympic committee members. He will leave before the vote, which now may be building in Chicago's favor.
"The impact of his presence in the Chicago delegation is not multiplied by double -- this impact can be multiplied by 25," said IOC member Ottavio Cinquanta of Italy.
Marc Ganis, a Chicago-based sports consultant, said: "Chicago has a very substantial proposal, but Obama was the missing ingredient. He provides the charisma, the personal touch and effectively gives them a B12 shot of charisma, which is needed when one compares Chicago's bid to Rio's."
A recent IOC site report gave the highest marks to Rio, and sentiment had appeared to be moving toward the city because South America has never hosted an Olympics. But some political operatives said that given the stakes, the White House must be confident that Chicago stands a strong chance.
"The risk is that the Olympics committee does the unthinkable and says, 'Sorry, Charlie,' " said Phil Singer, a Democratic political strategist based in Washington. "But the White House wouldn't be sending him if it wasn't feeling good about his prospects.
"No political operation worth its salt would allow its principal to go if it didn't feel fairly bullish about his chances for success."
The White House dismissed suggestions that it has any inside information.
Asked whether the White House had been led to believe a presidential visit might boost Chicago's chances, Gibbs said: "Well, I certainly hope that an appearance wouldn't hurt it. But we have gotten no intelligence on that."
At a fraught moment in both domestic and foreign affairs, some political strategists and GOP lawmakers said the timing is poor.
"With all the pressing issues we're facing right now, I think hopping off to Copenhagen is problematic," said Mark McKinnon, a Republican media consultant who worked for President George W. Bush. "People elected Obama to be president -- not the head of the Illinois Chamber of Commerce."
No shortage of work faces Obama.
Healthcare legislation is moving through committees, though a bipartisan agreement is proving elusive.
The U.S. and its allies are confronting intelligence reports that Iran is covertly building an underground facility capable of producing nuclear weapons. The U.S. is expected to demand that Iran cooperate more fully with inspectors at a meeting on Thursday in Geneva.
The White House also is reevaluating its strategy in Afghanistan, where the top U.S. commander, Gen. Stanley A. McChrystal, has warned in a confidential memo that without an infusion of forces, the war will be lost.
In an interview, Sen. Christopher S. Bond (R-Mo.) said Obama was neglecting warnings from McChrystal, while heaping too much time on Chicago's Olympics bid and frivolous appearances.
"I find it baffling that he has time to go to be on Copenhagen, to be on the [David] Letterman show and almost every other channel except the Food Network and Fox, but he doesn't have time to talk to Gen. McChrystal," Bond said.
An Obama spokesman said the president had indeed consulted McChrystal. Also, Obama has gotten a weekly written report from McChrystal and plans to speak to the general this week as part of the broad Afghanistan review that is underway.
"What does Sen. Bond have against the Olympics coming to America?" asked spokesman Tommy Vietor.
Katherine Skiba and Philip Hersh of the Chicago Tribune contributed to this report.