Barack Obama last night secured the prized endorsement of his former presidential rival, John Edwards, snuffing out the doubts that again afflicted his campaign after a crushing defeat on Tuesday night in West Virginia’s primary.

Mr Edwards had been courted heavily by both Mr Obama and Hillary Clinton after dropping out of the race more than three months ago, not least because of his strong appeal among white working-class or rural voters.

Last night he finally came off the fence, arriving at Mr Obama’s rally of 12,000 people in Grand Rapids, Michigan, to a deafening ovation and a warm embrace from the candidate himself.

Mr Edwards began his speech by paying tribute to Mrs Clinton as a "woman made of steel" whose had made America, the Democrats - and even Mr Obama - stronger. But the boos that greeted mention of her name suggested gave some indication of the task ahead in uniting the party before November's general election.

Mr Obama's insurmountable lead among delegates mans he has spent the past week being treated as a presumptive presidential nominee and Mr Edwards declared: “Brothers and sisters, we must come together as Democrats. We are here tonight because the Democratic voters have made their choice, and so have I.

“There is one man who understands that this is the time for bold leadership. One man who knows that to create lasting change you have to build from the ground up. One man who knows in his heart that it's time to create one America, not two. And that man is Barack Obama.”

Mrs Clinton’s 41-point rout of Mr Obama in West Virginia had earlier reinforced doubts about whether Mr Obama would be able to win votes from the traditional Democratic party base even as he cruised on towards the nomination.

Although facing near-impossible odds, Mrs Clinton had declared that she “never gives up”. She said that her battle with Mr Obama was far from over and the thumping win on Tuesday night had made her “more determined than ever to carry on”.

The result in West Virginia shows that a gaping wound has opened in Mr Obama’s electoral appeal — one, perhaps, that Mrs Clinton feels only she can heal. “The bottom line is that the White House is won in the swing states and I am winning the swing states,” she said at her victory party in Charleston.

Some of the crowd in Charleston held hand-made signs reading: “Until the last dog dies” — Bill Clinton’s fighting words when he was written off during the 1992 primary.

One supporter wore boxing gloves, another waved a bowling pin to symbolise the working-class pastime at which Mr Obama failed last month. Larry Garell, 37, said that he would not vote for Mr Obama in November’s general election. “He does not have the American flag wherever he goes. That means something around here. I’m not even sure he is American.”

Others questioned his “religious affiliation” as they repeated false rumours that he was a secret Muslim. Still more denied that their doubts about him were racially tinged and bridled at the media’s portrayal of their overwhelmingly white and rural state as being filled with “uneducated hicks”.

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