America was today rolling out its biggest guns to support Chicago's bid to host the 2016 Olympic Games.

Michelle Obama arrived in Copenhagen to lobby members of the International Olympic Committee, two days before the crucial vote.

The First Lady has offered to speak individually with as many members of the IOC as she can, in private tête à têtes at the Marriott Hotel. She is staying at the US ambassador's residence.

She will be joined by President Obama on Friday, for the last push to promote the couple's home city above the rival claims of Rio de Janeiro, seen as Chicago's nearest rival, and Madrid and Tokyo.

Mr Obama is the first incumbent US President to come in person to try to influence the choice of the 100 IOC delegates. With Chicago the front-runner after an ill-tempered campaign, he hopes to continue the trend for political leaders to swing the vote for their country, including Tony Blair for London 2012 and Vladimir Putin for the 2014 Winter Olympics in Sochi.

His presence at the vote is however a political risk.

“It is a brave thing he (Obama) is doing by coming here as if Chicago lose the personal fallout for him will be enormous,” said a source close to the IOC.

“A victory here would be of some benefit to him, but a defeat would have far more impact for his political enemies back in the United States."

Rio's chances are said to have receded a little because Brazil is already due to host the 2014 football World Cup, and the IOC fears Rio could immediately run into problems with attracting sponsors for 2016.

By comparison, London was able to hit the ground running as soon as it won in 2005 because the 2012 Games had no other future major sporting events to compete with.

“It is a case of whether the IOC want to play second violin in the orchestra or not," said the IOC source.

Rio would be the first South American city to host the Olympics – another fact which might worry the committee, as progress towards the Sochi games – another step into the unknown - has not been smooth.

“The question now is do the IOC want to take on board another unknown quantity in Rio," said the source.

One unlikely group rooting for Rio is a bunch of disgruntled Chicago taxpayers who fear that the corrupt bureaucracy of America's third largest city will bungle the business side of the event and leave residents with a large bill.

“I know it’s going to cost us money somehow,” said Joseph Patrick, 51. “The government doesn’t have a job (so) the only place they can get money is from us.”

A new Web site, www.chicagoansforrio.com, is the talk of the town and features the game “Match the Olympic host with its estimated budget overrun”. About 170 protesters marched outside City Hall on last night, many insisting that the games will push people from their homes, trigger more corruption and raise taxes.

“I don’t believe anything the city and the 2016 committee says,” said Larry Rivkin, who grew up in Chicago.

A poll released this month by the Chicago Tribune showed residents almost evenly split, with 47 per cent in favour of the bid and 45 per cent against – a steep drop from the 2-1 support the newspaper found in a February poll.