Senior Democrats expressed growing distress yesterday over the acrimonious and protracted fight between Hillary Clinton and Barack Obama, amid fears that the eventual winner will emerge badly wounded and vulnerable to defeat against John McCain.

Mr McCain, having wrapped up the Republican nomination, is now free to raise money solely for the general election battle, while his Democratic rivals squander their huge financial advantage trying to destroy each other.

He made an unannounced visit to Iraq yesterday, before stops in Jordan, Jerusalem, London and Paris. He meets Gordon Brown on Wednesday and will pay a courtesy visit to David Cameron during a tour aimed at burnishing his national security and foreign policy credentials. On Thursday he holds a £500-a-plate lunch at Spencer House, built by an ancestor of the late Diana, Princess of Wales.

Democrats are particularly worried that their party's battle appears to be hardening along race, gender and class lines with the growing possibility of a chaotic and divisive nominating convention in August.

“There's so much blood. Women want the White House. Blacks want the White House,” Donna Brazile, campaign manager to Al Gore in 2000, an African-American and an uncommitted Democratic super-delegate, told the ABC This Week programme. “They don't know how it will end. It's so toxic.”

Richard Machacek, another of the party's 800 super-delegates — the congressmen, senators and party leaders who are likely to determine the contest — said that the intense rivalry was “everybody's worst nightmare come to fruition”.

Both sides are accusing each other of injecting race into the battle. On Friday Mark Penn, Mrs Clinton's chief strategist, declared that, if Mr Obama loses the next primary in Pennsylvania on April 22, he could not win the general election, a claim that not even Mr McCain is making.

With only ten contests left, it is unlikely that Mr Obama or Mrs Clinton can win enough elected delegates to clinch the nomination. Barring a serious blunder or catastrophic revelation that changes the race, Mr Obama is likely to emerge in June with more pledged delegates. He has long argued that super-delegates should rally behind the nominee emerging with the most pledged delegates, because that would be reflecting the “will of the people”. Mrs Clinton says that superdelegates should back whoever they believe to be the best candidate.

Mr Obama received a boost for his case yesterday when Nancy Pelosi, the Speaker of the House and the most senior Democrat on Capitol Hill, said that it would be damaging to the party for its leaders to buck the will of the elected delegates.

Mrs Pelosi, an uncommitted superdelegate who appears to be leaning towards Mr Obama, said: “If the votes of the superdelegates overturn what's happened in the elections, it would be harmful to the Democratic Party.” Her comments could nudge other uncommitted Democrats on Capitol Hill towards Mr Obama.

Mr Obama also increased his lead among elected delegates over Mrs Clinton by 14 after the latest allocation from the votes in Iowa and California. Yet he faces growing scrutiny over his relationship with Jeremiah Wright, his former pastor, who was dropped from his campaign at the weekend. Extensive video footage has emerged of Mr Wright making incendiary and racially charged attacks from the pulpit on Mrs Clinton, declaring “God damn America” and saying a week after the attacks of September 11, 2001, that “America's chickens are coming home to roost”.

Mr Obama called the comments “appalling”. Yet despite attending Mr Wright's church for 20 years — the man married him, baptised his children and has been named his spiritual mentor — Mr Obama said that he learnt of the incendiary sermons only recently and had never witnessed one himself. Many commentators on both sides of the political divide found the claim difficult to believe, leaving the issue a significant problem for Mr Obama.

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