Barack Obama has a problem. Nearly a quarter of Democrats who hold a negative view of him believe he is a Muslim, according to a poll published by Pew Research on Thursday. Yet most Democrats who think negatively of Mr Obama also disapprove of his link to Jeremiah Wright, the pastor who introduced him to Christianity two decades ago.

Ten days after he delivered what many described as a historic speech on race, Mr Obama’s relationship with the black community still remains an issue. Although Hillary Clinton has largely avoided the topic – other than to say that she would not have chosen Mr Wright as her pastor – critics on the right have signalled it will be given a fuller airing in the general election if Mr Obama is the nominee.

This week Pat Buchanan, a former Republican contender, wrote: “America has been the best country on earth for black folks. It was here that 600,000 black people, brought from Africa in slave ships, grew into a community of 40m, were introduced to Christian salvation, and reached the greatest levels of freedom and prosperity blacks have ever known.”

Mr Buchanan added: “Wright ought to get down on his knees and thank God he is an American . . . We hear the grievances, where is the gratitude?”

In a comment condemned by Mr Obama, Mr Wright, now retired as pastor of the Trinity United Church of Christ in Chicago, had said “God damn America”. He also referred to the US of KKKA, after the Ku Klux Klan. 

Meanwhile Rush Limbaugh, the popular radio host, took offence at Mr Obama’s reference to his white grandmother, whom Mr Obama cited as having racist views typical of white people but whom he could no more disown than he would Jeremiah Wright.

“Obama has thrown his grandmother under the bus, and then drove the bus backwards and ran over her by calling her a typical white woman,” said Mr Limbaugh.

“It is clear that Senator Obama has disowned his white half . . . He’s decided he has got to go all in on the black side,” he added.

Conversely, commentators on Fox News, the conservative television channel, took offence on behalf of white people in general rather than Mr Obama’s grandmother in particular, to such an extent that Chris Wallace, a Fox anchor, came on air and berated his colleagues for lacking in balance.

“It seems to me that two hours of Obama-bashing on this ‘typical white person’ remark is somewhat excessive,” said Mr Wallace, who pointed out that the show neglected to mention Mr Obama’s speeches on Iraq and the economy – both delivered in the previous two days.

Supporters of Mrs Clinton, whom many now give only a very slim chance of surpassing Mr Obama’s lead among elected delegates, admit privately that her best chance of winning the nomination is to persuade the party’s unelected “super-delegates” to overturn the popular vote, by convincing them that Mr Obama would be defeated by the Republican candidate John McCain in November’s general election.

Some polls suggest that Mr Wright’s more factious remarks, which are likely to continue dribbling out for months, have not done Mr Obama lasting damage. According to Pew, Mr Obama’s lead over Mrs Clinton is as wide as it was in late February. Both continue to lead Mr McCain narrowly in general election polls.

But according to a Gallup poll on Thursday, the proportion of Mrs Clinton’s supporters who say they will not vote for Mr Obama if he is the nominee is much higher than the other way round – 28 per cent against 19 per cent. This presents Mrs Clinton with her own dilemma. “There is no way she can say to fellow Democrats that Obama is unelectable because of the race issue,” says one Clinton supporter. “But in the absence of any other weapon it may become irresistible.”

Donna Brazile, a senior Democratic official who was the first black woman to manage a Democratic campaign, for Al Gore in 2000, argues that the Obama-Wright issue is more likely to surface in an election year that is considered unfavourable for Republicans. “Wright fits with their narrative of division, diversion and distraction,” she says.

Bill Galston, a veteran of Walter Mondale’s losing 1984 Democratic campaign, says it is too early to tell what impact Mr Obama’s speech will have on voters.

Mr Galston likened the speech to the Rorschach test, named after the psychologist who observed people’s diverse reactions to spreading ink blots. “Everybody sees something different – you read what you want into it,” says Mr Galston. “How America reacts to the speech will tell us more about America than about Barack Obama.”