Jeremiah Wright re-emerges to say his church has been threatened with attack just as the Democratic race heads for its last big contest

Racial divisions loomed over the Democratic race last night as Senator Barack Obama's controversial pastor Reverend Jeremiah Wright admitted his church has received bomb threats.

Wright, whose fiery sermons on America and race relations have stirred anger among some critics, has re-emerged into the headlines just as Obama and Senator Hillary Clinton kick off 10 days of campaigning in Indiana.

In his first interview since videos of Wright preaching began a storm of recrimination, Wright was asked by PBS journalist Bill Moyers if he had received death threats. 'Yes ... and bomb threats at the church,' Wright replied. 'What have we gotten into here? People ... telling us how they are going to wipe us off the face of the earth in the name of Jesus.' He also described how journalists had been harassing church members, including one who was dying in a hospice.

In the lengthy interview, Wright defended his criticisms of America, which included saying: 'Not God Bless America, God damn America.' He said his remarks had been misinterpreted by the media and defended his church's record in helping Chicago's poor.

Wright has undoubtedly been the biggest thorn in Obama's side during his campaign to be America's first black president. The controversy derailed Obama's plans to run a 'post-racial' campaign and forced him into a landmark speech on race in America. That was aimed at settling the issue, but since then the contest has become increasingly racially polarised.

Clinton has been successfully wooing white working-class voters in states such as Pennsylvania and her supporters point out such a voting bloc will be crucial in November's general election. They are also crucial in Indiana, the last competitive state in the contest and Obama's last real chance to knock Clinton out of the contest before the party convention.

Wright's return to the headlines as the contest moves into Indiana is undoubtedly a blow to Obama's chances. Nor is Wright likely to disappear from the headlines. He has two more interviews scheduled this week, including an address to the National Press Club in Washington DC. That will add fuel to a fire of negative attacks on the campaign trail.

The past two weeks have seen almost unprecedented levels of negativity as Clinton seeks to prove that she is a better candidate, despite trailing Obama in both the popular vote and the delegate race. She has staked her whole strategy on persuading so-called superdelegates - top party officials and politicians - that they should give the nomination to her because Obama cannot beat Republican nominee John McCain.

However, some feel that if Clinton's strategy succeeds, the Democrats will terminally alienate the black voters who have flocked to Obama and represent the most solid voting bloc of Democratic support in a general election. They also feel that, even if Obama becomes the nominee, he will have been fatally weakened by Clinton's attacks, which are already being mimicked by Republican operatives. 'If this continues on its current course [the damage] will be irreparable,' Congressman James Clyburn told the Washington Post. Clyburn is the highest ranking black politician in Congress and his remarks will be seen as a warning to tone down Clinton's attacks.

That appeal may fall on deaf ears. After months of attacks Clinton's team believe they have finally succeeded in raising enough questions about Obama to weaken him. A win in Indiana, they believe, will ensure Clinton can carry that fight all the way to the Denver party convention in August where she will try to rally superdelegates to her side.

An Obama win would be his best chance to knock her out and show that he can win working-class white voters. Polls have put the two virtually neck and neck in the state which goes to the polls on 6 May. However, the most recent surveys show Obama opening a slight lead.