Barack Obama's surge is beginning to loosen Hillary Clinton's grip on the Democratic super-delegates who may decide the outcome of their presidential race.

Congressman David Scott announced yesterday that he was defecting from Mrs Clinton's camp, saying he needed to represent “the wishes of my constituents” — 80 per cent of whom had backed Mr Obama in Georgia's primary. Another black Congressman, John Lewis, a civil rights hero whose views carry huge weight, denied reports that he had already abandoned Mrs Clinton. But he is still considering a switch with colleagues saying that he felt increasingly torn about his earlier endorsement.

“It could [happen]” he said. “There's no question about it. It could happen with a lot of people ... we can count and we see the clock.” Mrs Clinton, trailing Mr Obama in the overall delegate count, still has the edge among super-delegates who many expect to hold the balance of power at the nominating convention in August.

But several of her supporters have moved to Mr Obama's camp or the ranks of the undecided after Mr Obama's eight straight victories of the past week.

A race like a crackpot Dynasty

The contest between Barack Obama and Hillary Clinton matches any fiction

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Mrs Clinton arrives belatedly in Wisconsin today for three days of campaigning, after a decision by her strategists that her fightback against Mr Obama must begin in the state's primary on Tuesday. Aides fear that Mr Obama's momentum could become unstoppable if she cedes yet another state before the critical primaries on March 4 in Texas and Ohio. They believe that Wisconsin's heavily white, blue-collar, economically stressed electorate offers her a chance of defying expectations by running Mr Obama close or even winning.

Bill and Chelsea Clinton have campaigned in Wisconsin for three days, while the former First Lady launched a statewide television advertisement attacking Mr Obama.

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