The president and his wife, fellow Chicagoan Michelle Obama, put their capital behind an enormous campaign to win the Olympics bid. Never before had a US president made such an in-person appeal.
"I urge you to choose Chicago," Obama told members of the International Olympic Committee.
"And if you do _ if we walk this path together _ then I promise you this: The city of Chicago and the United States of America will make the world proud," the president said.
Chicago, Rio de Janeiro, Madrid and Tokyo have been making their cases to the IOC for more than a year, but many IOC members were believed to be undecided about which city they would vote for Friday. Some said they might not decide until after the cities made their final presentations in Copenhagen.
Both Obamas spoke on deeply personal terms about Chicago, the city at the center of the world's spotlight so many times, including in November when Barack Obama won the White House and stood proudly with his family.
The president described Chicago as a place of diversity and warmth.
"Chicago is a place where we strive to celebrate what makes us different just as we celebrate what we have in common," he said. "It's a place where our unity is on colorful display ... It's a city that works from its first World's Fair more than a century ago to the World Cup we hosted in the nineties, we know how to put on big events."
For all the anticipation surrounding Obama's appearance in Copenhagen, his arrival at the IOC meeting was decidedly subdued.
The 100-plus committee members, who had already been warned not to show bias during the presentations, sat silently as the Obamas walked into the Bella Center with the rest of 12-member Chicago delegation.
Michelle Obama gave a passionate account of what the games would mean to her father, who taught her as a girl how to throw punches better than the boys. She spoke of fond memories of growing up on the South Side of Chicago, sitting with her father and cheering on Olympic athletes.
She noted that her late father had multiple sclerosis, so she knows something about athletes who compete against tough odds.
"Chicago's vision for the Olympic and Paralympic movement is about so much more than what we can offer the games," she said. "It's about what the games can offer all of us _ it's about inspiring this generation and building a lasting legacy for the next."
The president anchored the US charm offensive.
He referenced his own election as a moment when people from around the world gathered in Chicago to see the results last November and celebrate that "our diversity could be a source of strength."
"There is nothing I would like more than to step just a few blocks from my family's home and with Michelle and our two girls welcome the world back to our neighborhood," Obama said. "At the beginning of this new century, the nation that has been shaped by people from around the world wants a chance to inspire it once more."
After the Obamas' comments, the US delegation fielded questions from committee members, and at one point the president jumped in. He said he envisioned that the Chicago games would allow the United States to restore its image as a place that, at its best, is "open to the world."
He emphasized that the White House and the State Department would put their full weight behind making sure international visitors "feel welcome and will come away with the sense of the incredible diversity of the American people." And Americans, he said, will be reminded of their links to the rest of the world.