Watch it, Brown – Cameron is after that Obama magic

Followed by plaudits from an ageing Edward Kennedy, Obama, in trademark orange tie and slim-cut, single breast black suit, spellbinds with his prophetic style. He is so confident in his oratory that he mocks his own powers: "My mother now tells me, 'You must be a talker not a doer, you've got your head in the clouds'." Alongside leftist anti-war rhetoric he spits soundbites that would startle a Labour audience: "I love capitalism."

The enraptured crowd yells back his campaign slogan of "Yes We Can", which to cynical British ears reminds one irresistibly of Bob the Builder. (Can we fix it? Yes we can.)

All the candidates in this race are larger than life. Obama's youthful autobiography, Dreams from My Father, is one of the few politicians' works in the language worth reading for its prose and charm; Clinton is awesomely well briefed on every issue. In the Republican camp, Mitt Romney, the Mormon who dropped out of the race on Thursday, is a self-made multi-millionaire who really can fix anything in the real world from a broken business to a bust winter Olympics. Mike Huckabee beats Ken Clarke as the man you would most like to have a beer with, and the frontrunner John McCain is a genuine war hero.

A British prime minister and opposition leader should welcome working with any of them. Both Gordon Brown and David Cameron will be happy to see the back of President Bush too. Neither Labour nor Conservatives have prospered by backing the Iraq war.

But the three frontrunners do offer alternatives. The former Bush phrase maker, David Frum, (he coined the "axis of evil") put it to me like this: "McCain sees himself as commander-in-chief of the world; Obama is first citizen of the planet; and Hillary Clinton is . . . [wait for it] architect of the universal US health plan."

With her eye for policy minutiae and risk avoidance Clinton will be the perfect soulmate for Brown. "They know each other, they have been in contact over the years," says a supporter. Brown's droning interviews

on the Today programme will be matched by Clinton's tin foil on tooth filling gushing "town hall" meetings. One commentator dismisses her so: "Hillary has taken statesmanlike, moderate positions on all the issues because she thought she was a shoo-in for her party nomination. That's screwed her."

A Hillary foreign policy man observes that a Clinton or Obama presidency would step up Nato's efforts in Afghanistan. Because of Bush's unpopularity with their voters, the Europeans have shirked doing their fair share. Either way Brown will greet a Democrat president with "a deep sigh of relief".

Certainly style will change. But substance? "In all important hot button issues America is not going to change. In the end the American body politic operates in a very narrow bandwidth," claims Danielle Pletka of the American Enterprise Institute.

But Obama wants to give America's enemies, even Ahmadinejad of Iran, a second chance. Here he is quoting JFK: "We should never negotiate out of fear, but we should never fear to negotiate." This sounds a shade Jimmy Carter-ish for those old enough to remember the former peanut farmer's first faltering steps in office. Pletka is doubtful that Obama's commitment to pull all US soldiers out of Iraq by 2009 will last: "The centre of gravity here is not cut and run. If he runs on that he will lose in the general election."

Brown and Cameron's talk about challenging their parties is exactly that; John McCain really has enraged his own party on everything from campaign finance reform to immigration. Our prime minister has compiled a bland volume about Courage; the Republican frontrunner's life writes the book. Any Briton brought up on Our Island Story tales of heroism - Sir Philip Sidney's dying refusal of water because "thy need is greater than mine" springs to mind - will warm to a man who refused to leave the Hanoi "Hilton" until his comrades were set free, despite suffering torture. Having met him, I can testify to his humour but not his reputation for bad temper.

McCain may be disliked by social conservatives but he has fans among the neocons, demonised in Britain as warmongers. That may worry Brown and the Foreign Office. McCain has pledged to stay "a thousand years" in Iraq if necessary; on Iran, his hawkish views trouble the pacific minded. Nile Gardiner, director of the Margaret Thatcher Freedom Centre of the Heritage Foundation, judges: "If the UK

did not stand shoulder to shoulder with the US in a conflict with Iran that would have serious implications for the special relationship."

As for the Tories, one in high command says approvingly: "We all know McCain and he knows us, Conservatives are closer to him than to the White House." The Republican gave a keynote speech to the Tory party conference last year. He is Cameron's ally on climate change, and defends civil liberties against the excesses of the war on terror: McCain has attacked the use of torture like no other US politician. They may disagree over liberal interventionism abroad: Cameron worries about 'dropping democracy from a bomb bay.' One disgusted American critic claims: "David Cameron is to the left of most Democrats." Obama and Clinton can live with lower taxes and tougher welfare reforms than our opposition will ever contemplate.

But despite the foreign policy wonks' doubts, Obama, the unknown, is the star of this contest. Comparisons have been made to Jack and Bobby Kennedy. But in the Third World, a President Obama could be greeted as a younger Nelson Mandela. Even hostile Muslim opinion will be intrigued: "Barak" means blessed in Arabic (his Kenyan, Luo tribe, grandfather was Muslim) and he has first-hand experience of Islam from his boyhood in Indonesia. He would wield enormous "soft-power" in the First World, too, especially among those classes who dance to Bono and Bob Geldof's tunes. So that includes Brown too.

Cameron is also intrigued by Obama's glamour. Tory modernisers see an obvious parallel in his message "I want to be part of the future not the past". The Cameroons, like him, want to move on from the old ideological battles. Obama transcends Vietnam and the culture wars; the Tory "Obamaniacs" think the polarising private versus public sector dichotomy of the 1980s is old hat. "The Obama argument is a very powerful one that we will adapt," says the Tory bigwig. The critics will demand of both "where's the beef?"

"Change does not happen from top down, it happens from the bottom up." These anti-statist words were Obama's, but could have come from Cameron. This language doesn't come naturally to Clinton or Brown. For "empowerment" is not an old liberal, pro-government message; it is a plea for self-help - in American parlance, a hand-up not a hand-out.

Obama, the visionary, is running for president. Clinton feels like she could be a British prime minister. I don't presume to predict whom Americans will pick for their president, but Obama is one of those rare politicians who make voters feel better about themselves. We glimpsed it here in the young Tony Blair . . . and didn't he go far?