Within hours of Barack Obama finishing his speech about race relations on Tuesday, many commentators had declared it a triumph.

Chris Matthews, an MSNBC host, called it "one of the great speeches in American history" and "worthy of Abraham Lincoln".

"This should be, to me, an American tract," he said. "Something that you just check in with, now and then, like reading Great Gatsby and Huckleberry Finn."

But while liberal and mainstream observers were almost unanimous in their praise, it remains unclear whether the speech achieved its political objective.

Mr Obama sought to limit damage from divisive comments by Rev Jeremiah Wright, his former pastor.

News organisations had unearthed video of angry tirades by Mr Wright against white racism in sermons to the United Church of Christ in Chicago, which Mr Obama has attended for 20 years.

Among his remarks were suggestions that the US had brought the September 2001 attacks upon itself and was responsible for spreading the HIV virus among blacks.

The conventional political response would have been for Mr Obama to put as much distance as possible between himself and Mr Wright. Mr Obama did the opposite. He repudiated the pastor's "profoundly distorted view of America" but said he could "no more disown him than I can my white grandmother", who he said had once confessed to a fear of black men. Mr Obama said the US must address the root causes of his pastor's anger and his grandmother's prejudice, however misguided both may be.

Commentators praised his courage in refusing to deflect the controversy and instead confronting race - one of the thorniest issues in US politics - head on.

While it may have been a masterful piece of oratory, however, some experts believe it could also turn out to be a political suicide note.

"Only a tiny fraction of Americans will ever see the speech in full. Once it went through the media sausage grinder all you were left with was him failing to disown the pastor," says Michael Munger, political scientist at Duke University and a libertarian. "It showed he is the kind of candidate we should want as president but not the kind we tend to elect."

Until this week, Mr Obama had seldom talked directly about race on the campaign trail, allowing him to appeal across racial boundaries in a way that previous African-American presidential candidates did not. The more he is forced to talk about race the more he risks becoming defined as a black candidate.

"It undermines how Barack Obama has tried to position himself," says Tony Fabrizio, a Republican strategist. "There was no soundbite in the speech to compete with Wright saying, 'God Damn America'. It allows us to define the speech."

Hillary Clinton, Mr Obama's Democratic rival, has been careful to avoid exploiting the controversy. But it could solidify her support among white Democrats and sow doubts among superdelegates - the senior Democratic officials whose votes look likely to decide the nomination - about Mr Obama's electability.

Mr Fabrizio says the Wright affair has caused many conservatives to reconsider the conventional wisdom that Mrs Clinton would be the easiest opponent for John McCain, the Republican candidate, in November. "The Wright controversy has shown a lot of Republicans that this guy has a glass jaw," he says.

Mr McCain is expected to steer clear of the issue to avoid being accused of playing the race card. But Republicans outside of the official campaign are likely to be less reticent. "McCain doesn't need to go near it because he has YouTube doing the job for him," says Mr Fabrizio, referring to the video-sharing website where Mr Wright's sermons have been viewed by millions.

"Pastor-gate" is one in a series of incidents that conservatives have used to question Mr Obama's patriotism. "Republicans are beginning to sew together a narrative," says Jamal Simmons, a Democratic strategist.

Commentators have drawn a comparison between the Wright sermons and the "Swift Boat" advertisements that badly damaged John Kerry, the 2004 Democratic nominee, by questioning his war record in Vietnam.

"Kerry had been in Vietnam. Bush was not. Yet still the Republicans managed to make Kerry look unpatriotic," says Mr Munger. "This time Obama is running against a real war hero in McCain so the Republicans have an easier task."

But Mr Simmons cautions against assuming the controversy will take a similar course. "There has been so many things about this election that have been unprecedented and unpredictable," he says. "It is too soon to say how this will play out."

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