US:Barack Obama's campaign has claimed that it is now "next to impossible" for Hillary Clinton to reclaim the lead in pledged delegates to the convention that will choose the Democratic presidential nominee.
Mr Obama's campaign manager, David Plouffe, said the Illinois senator's sweeping victories on Tuesday in Virginia, Maryland, and the District of Columbia gave him a lead of 136 in pledged delegates. "We have created such a buffer in terms of the pledge delegate lead that we think it is highly unlikely that it will be eroded," he said.
"It is next to impossible for Senator Clinton to close that pledge delegate count. The only way she can do it is win contests by 25 to 30 points. And we don't see contests were she can do that."
Mr Obama expects to win again next week in Wisconsin and Hawaii, giving him an unbroken succession of 10 victories since Super Tuesday. Mrs Clinton will campaign in Wisconsin early next week but her chief strategist, Mark Penn, said yesterday that he is not expecting a major improvement in her fortunes until Texas and Ohio vote early next month. "We expect change to begin on March 4th."
The scale of Mr Obama's victories on Tuesday, when he won two out of three votes in Virginia and Maryland and three out of four in DC, confirmed his position as Democratic frontrunner. He is now ahead in the total delegate count (including super delegates), in the popular vote and in the number of states won.
Mr Obama's campaign is also far ahead of Mrs Clinton's in terms of money, momentum and enthusiasm and Tuesday's primaries saw him challenge Mrs Clinton's grip on Hispanics, working class whites and even women.
"This is what change looks like when it happens from the bottom up," Mr Obama told a rally of 17,000 people in Wisconsin. "This is the new American majority."
Campaigning in Texas, Mrs Clinton insisted that the race remained competitive despite her recent setbacks, pointing out that each candidate's fortunes have shifted a number of times since the voting started.
In a sign of his new status as front-runner, Mr Obama has been avoiding debates with Mrs Clinton, agreeing to only two before March 4th. In a new TV advert airing in Wisconsin, Mrs Clinton claims that Mr Obama is reluctant to answer direct questions about his policies.
"Maybe he'd prefer to give speeches than have to answer questions. Like why Hillary Clinton has the only healthcare plan that covers every American, and the only economic plan that freezes foreclosures. Wisconsin deserves to hear both candidates debate the issues that matter," the advert says.
John McCain won all three Republican primaries on Tuesday, fighting off a strong challenge from former Arkansas governor Mike Huckabee. Mr McCain went to Capitol Hill yesterday to rally congressional support for his candidacy.
Republican house leader John Boehner said he was willing to set aside differences to support Mr McCain as the candidate most likely to win in November.
Mr McCain used his victory speech on Tuesday to target Mr Obama, ridiculing the Illinois senator's trademark invocation of hope. "Hope, my friends, is a powerful thing. I can attest to that better than many, for I have seen men's hopes tested in hard and cruel ways that few will ever experience," Mr McCain told supporters in Alexandria.
"To encourage a country with only rhetoric rather than sound and proven ideas that trust in the strength and courage of free people is not a promise of hope," he added. "It is a platitude."
Mr McCain is almost certain to win the Republican nomination, but Mr Huckabee still shows no sign of leaving the race and he made clear this week that he has no interest in any elected office other than president.
"There's a greater chance that I would dye my hair green and get tattoos all over my body and do a rock tour with Amy Winehouse than there is that I would run for the Senate," he said.