The Republican presidential hopeful's fundraising visit to Britain was meant to be a chance for the former Massachusetts Governor to display a foreign-affairs gravitas that would help to sell his claim to the White House.
But rather than flaunting his statesman-like credentials, Mr Romney managed to insult his hosts and commit that cardinal sin of US politics – "flip-flopping" – all within hours of landing in Britain. In unguarded and far-from-diplomatic language, Mr Romney initially questioned London's commitment and ability to stage the Games. In an interview with US television, he said he had noticed "disconcerting" signs that Team London was not ready. "It's hard to know how it will all turn out," he said.
Mr Romney's comments on Olympic organisation carry weight. As the capitalist guru who saved the Salt Lake City Winter Olympics from financial ruin, he can claim to know a thing or two about staging the world's biggest sporting event.
His comments prompted a sharp rebuke from David Cameron, who said: "We are holding an Olympic Games in one of the busiest, most active, bustling cities anywhere in the world. Of course it's easier if you hold an Olympic Games in the middle of nowhere."
But hours later, after a private one-to-one with Mr Cameron at No 10, Mr Romney appeared miraculously converted and predicted that London 2012 would be a "very successful" Olympics. In the summer sun in Downing Street, attempting to put the morning's mistakes behind him, Governor Romney focused on beach volleyball. "As I look out of the back side of 10 Downing Street [I] see a venue having been constructed. Knowing that athletes will be carrying out their activities almost in the backyard of the Prime Minister is really quite an accomplishment."
His U-turn apparently went unnoticed by Boris Johnson, however, who had his own retort to Mr Romney's doubts about London's readiness. Speaking in front of 60,000 people at a concert in Hyde Park to mark the end of the Olympic Torch relay, the Mayor of London shouted: "There are some people coming from around the world who don't yet know if we are ready."
"There's a guy called Mitt Romney who wants to know whether we are ready. Are we ready? Yes, we are!"
Mr Romney's day of gaffes did not end there. After a meeting with Tony Blair in his Brook Street offices in Mayfair, he greeted Ed Miliband in his Commons office as "Mr Leader" – leading some to wonder whether he had forgotten the Labour leader's name. "My right honourable friend" would have been amusing, though "comrade" isn't in the Republican lexicon.
The Romney campaign may not judge London as a failure if the £75,000-a-plate fundraising dinner held last night in Mayfair delivers millions of dollars into the Republicans' coffers.
Raising big bucks for what is expected to be the most expensive bid for the White House in history means picking the pockets of rich Republicans who have high-wealth profiles in London's financial district.
Of those attending the private fund-raiser – where all were asked to bring their US passports to ensure compliance with US election rules – some are reported to have donation track records that go back to Ronald Reagan, John McCain, Dick Cheney, and both George Bush Snr and Jnr.
City rumours that the gaffe-punctuated day had reduced the plate-rate fee were dismissed by campaign insiders as "mischievous". Among the key co-hosts for a fundraising supper in Mayfair last night were: Eric Assimakopoulos, the founder and managing director of Revetas Capital Advisers; Scott Collins, from Summit Partners; and Dwight Poler, from Bain Capital Europe.
Karin Robinson, vice-chairwoman of the Democrats Abroad organisation, said: "These bankers are being asked to write cheques for Mitt Romney because they know that if he wins they get to write their own rules. These millionaires and billionaires are being promised generous tax cuts while the rest of us are struggling."
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