You might want to remember what happened in American politics this week for a very long time.

I'm not talking about the spectacle of the remaining members of the Kennedy dynasty jumping on to the Barack Obama bandwagon (whatever you do, Senator, don't give Teddy the keys). I'm not talking about the historic certainty now that John Edwards, the sole remaining white guy, has quit the race, that either Senator Obama or Senator Hillary Clinton will be the Democratic Party's nominee. I'm not thinking about the Democrats at all.

I'm talking instead about the quiet revolution that has overthrown the old order in the Republican Party. We have witnessed nothing less than a bloodless coup this week that promises to have ramifications for America perhaps even larger than the prospect of a black or a woman president.

Forget everything you thought you knew about the Republicans. Forget the party of God, guns and gays. The brief, and let's be honest (especially those of us who once rather approved of him) catastrophic era of the Bush Republican Party is certainly over. But more than that, Senator John McCain's victory in the Florida Republican primary and what has followed has buried not just the Bush presidency but the Republican Party of the past couple of decades.

A race like a crackpot Dynasty

The contest between Barack Obama and Hillary Clinton matches any fiction

Multimedia

• Full coverage: US elections

BACKGROUND

• The ascent of Barack Obama, Mr Charisma

• Decay, jobs and guns fall under the spotlight

• Free trade: Clinton/Obama's mistakes

Barring some miracle now, Mr McCain will win comfortably next week's Super Tuesday primaries and be more or less confirmed as the Republican presidential nominee.

It is true, as I have argued before, that Mr McCain is not the louche liberal that his Republican enemies would have you believe. He has a strong conservative record on issues such as abortion and, of course, on national security.

But there can't be any doubt that, if given the chance to be president, Mr McCain will govern in a fundamentally different way from either Mr Bush or the Republicans who have dominated Congress for the past decade or more. He does not believe in the modern theology that taxes must always be cut, whatever the circumstances or the consequences. He doesn't think America can survive by closing its doors to immigrants. Though there is no stronger supporter of the War on Terror, he believes that America's reputation has been badly damaged by the mistakes of the past few years - from Abu Ghraib to Guantanamo.

If you can judge a man by the company he keeps, you get a sense of where Mr McCain is going to take the Republican Party. This week he got three endorsements that will prove critical to his near-certain victory. First, the pivotal backing of Charlie Crist, the Governor of Florida. Mr Crist is one of the most wildly popular governors in America. He was one of the few Republican successes in the disastrous 2006 midterm election. He himself represents a kind of post-Bush era transition: he took over from Jeb Bush, the President's brother. Mr Crist has succeeded because he has governed from the Centre in a state that we have come to know can be crucial in presidential politics. You heard it here first, by the way - Mr Crist will loom large in the Republican Party; perhaps as Mr McCain's vice-presidential nominee; perhaps as presidential candidate himself one day. His gamble in supporting Mr McCain in Florida was critical to the senator's win there.

Then, on Wednesday, following the primary victory, Mr McCain was endorsed by Rudy Giuliani. If Mr McCain is a maverick in Republican politics, then Mr Giuliani is a sort of deranged mustang, stampeding about the political prairie, charging the high fences of conservative orthodoxy.

Then yesterday, in California, Mr McCain won the backing of Arnold Schwarzenegger, the Governor of California. Mr Schwarzenegger has, like Mr McCain, infuriated the Republican Right in his own state, with support for such measures as strong efforts to tackle climate change.

What these three have in common is that they all know that for Republicans to survive in the harsh political climate of the post-Bush years, they need to reach to the Centre.

Any obsequies for the Bush Republican Party will also need to include the campaign of Mitt Romney, for whom Super Tuesday will be a final stand. Mr Romney, oddly, was once a model of new, forward-looking Republicanism. Like Mr Schwarzenegger he had governed quite successfully in a state (Massachusetts) where Republicans seemed thinner on the ground than daffodils in November. But he consciously remade himself for this campaign as a traditional, immigrant-bashing, gay-baiting, Bible-toting (well, Book of Mormon-toting ) conservative. And it didn't do him much good.

The problem for the McCain Revolution is its dependence on the support of moderate Republicans and independents. Mr McCain has squeaked through to victory in three major primaries, winning less than 40 per cent of the vote in each.

Though he has a rare chance to show that he and his colleagues can govern from the Centre, Mr McCain will need the backing of conservatives to win. Yet the impossibilist, increasingly unhinged right wing of the party, the latter-day Bourbons who have learnt nothing and forgotten nothing from the past decade, are still a powerful force. They could, if they chose, destroy Mr McCain and the new Republican leadership with a guerrilla campaign for the next nine months.

But they'll need to be aware that the price for that victory may well be the destruction of the very party they will be claiming to save.

Times Recommends

• Graveyard of empires could claim more careers
• Would you live on the wrong side of the Berlin Wall?
• At last we’re getting our heads out of the sand