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Even in the midst of a final bombardment in the battle for the White House the sound of gunfire can be heard coming from behind Republican lines, presaging a protracted and bitter civil war.

A party that only four years ago appeared so disciplined and dominant as it delivered President Bush a second term is now divided in the face of an anticipated rout that may give Democrats unfettered power across Washington.

Mr Bush's legacy — unfinished wars, a tainted reputation for competence, record high spending, a global economic crisis and the effective nationalisation of the financial system — have shaken loose the ideological cement that once bound the Republican party together.

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This has left national security realists at odds with “neocon” hawks over Iraq, fiscal conservatives railing against the bailout of Wall Street, and the Religious right — “theo-cons” — skirmishing with the party leadership over what it regards as a too-timid approach on issues such as abortion, civil partnerships and illegal immigration.

Such fractures in the coalition, apparent in a primary campaign which John McCain won despite securing significantly less than half the vote, have become infected with gangrene during the presidential election.

Threatened with open revolt if he picked the independent Democrat Joe Lieberman as his running-mate, Mr McCain hoped to galvanise his party by choosing Sarah Palin. The result has been a dysfunctional campaign.

Some of his own advisers say that she is more intent on positioning herself for the next presidential race than fighting this one. Her defenders point out that it is she who pulls the crowds, not him, and suggest that Mrs Palin has been ill-served - even betrayed — by Mr McCain's team.

She is increasingly giving voice to the dissent in Republican ranks, criticising the decisions to pull the campaign out of Michigan and to avoid making racially combustible attacks on Barack Obama over his links with the Reverend Jeremiah Wright.

When she went to Iowa at the weekend, it may well have been significant that she hinted at support for ethanol subsidies which are opposed by Mr McCain but will put her in good stead when the state kicks off the presidential nominating process in 2012.

There is little doubt that as a populist pitbull champion of culturally conservative issues she excites core Republicans in a way that Mr McCain cannot, not least because the party has moved decisively to the Right over the past two decades. Mrs Palin is also coming to symbolise a fresh rift in the party between the base and the Establishment.

The list of Republicans backing Mr Obama includes not only centrist figures such as General Colin Powell, the former Secretary of State, but also Ken Adelman — a leading neocon who advised Donald Rumsfeld on Iraq and introduced Dick Cheney, the Vice-President, to Paul Wolfowitz, the hawkish former Deputy Defence Secretary.

Mr Adelman admits to being startled at finding himself in Democrat ranks, attributing his defection to doubts about Mr McCain's temperament and his “appalling lack of judgment” in picking Mrs Palin. He told The New Yorker magazine: “I would not have hired her for even a mid-level post in the arms-control agency.”

Christopher Buckley, whose father helped to found the modern conservative movement, has also swallowed his right-wing principles to back Mr Obama, contrasting the Democrat's “first-class intellect” with Mr McCain's decision to pluck Mrs Palin from the Alaskan wilderness. “What on Earth can he have been thinking?” he asked.

Mrs Palin promises to eschew the traditional hierachy even as she hints at having a very big part in the Republicans' future. “I would love to promote the party ideals if we're going to live out the ideals and maybe allow other American voters to understand what the principles of the party are,” she told The Weekly Standard magazine. “We've got to be assured we have enough people in the party who will live out those ideals and it's not just rhetoric. Otherwise, I'd be wasting my time.”

At one recent rally she said: “We believe that the best of America is not all in Washington, DC. We believe that the best of America is in these small towns that we get to visit, and in these wonderful little pockets of what I call the real America, being here with all of you hard-working, very patriotic, very pro-America areas of this great nation.”

Her problem is that with polls suggesting that North Carolina, Virginia and tracts of the Rocky Mountain West are heading into Mr Obama's columns, “real America” may no longer be big enough to elect a Republican president.

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