Barack Obama is close to overtaking Hillary Clinton in the race for Democratic delegates after sweeping victories at the weekend in Louisiana, Nebraska and Washington state, writes Denis Stauntonin Washington.
Former Arkansas governor Mike Huckabee has slowed John McCain's progress towards the Republican nomination by winning Kansas and Louisiana, although Mr McCain clung to a narrow victory in Washington state.
Mrs Clinton announced yesterday that her campaign manager, Patti Solis Doyle, is stepping down and will be replaced by Maggie Williams, the candidate's former top White House aide. The move surprised few in Washington as Ms Williams had played an increasingly prominent role in the campaign since the New Hampshire primary and a staff shake-up had been mooted for almost a month.
Mr Obama is already ahead of Mrs Clinton in pledged delegates - those chosen directly in primaries and caucuses - but she retains a slight edge when super-delegates are included. The 800 super- delegates are elected officials and senior party figures who are allowed to vote at the national convention that will nominate the Democratic presidential candidate in August.
The Associated Press estimates that Mrs Clinton has 1,095 delegates to Mr Obama's 1,070, including super delegates: 2,025 votes are needed to secure the nomination.
"We won in Louisiana, we won in Nebraska, we won in Washington state. We won north, we won south, we won in between, and I believe we can win Virginia on Tuesday if you're ready to stand for change," Mr Obama told an audience of cheering Democrats at a party dinner in Richmond, Virginia.
Mrs Clinton addressed the same dinner earlier, presenting herself as the candidate with the necessary toughness to defeat Mr McCain in November. "If I'm your nominee, you will never have to worry that I will be knocked out of the ring because I do have the strength and experience to lead this country. And I am ready to go toe-to-toe with Senator McCain whenever and wherever he desires," she said.
Mrs Clinton avoided criticism of her Democratic rival but Mr Obama spent much of his speech presenting her as an establishment politician who could not win the general election.
"The stakes are too high and the challenges are too great to play the same old Washington game with the same old Washington players and expect a different result.
"People want to turn the page. They want to write a new chapter in American history," he said.
Maine voted yesterday and Mr Obama hopes for three more victories tomorrow after primaries in Virginia, Maryland and the District of Columbia. Polls show Mr Obama ahead in all three primaries but Mrs Clinton has been campaigning vigorously in Virginia in the hope of an upset in that state.
If he wins this week's primaries, Mr Obama could for the first time move ahead of Mrs Clinton in the delegate count and the popular vote as well as the number of states won.
Mr McCain remains the prohibitive front runner in the Republican race, with a huge lead in delegates over Mr Huckabee but the former Baptist minister told conservative activists at the weekend that he still believes he can win.
"I know the pundits, and I know what they say - the math doesn't work out. Well, I didn't major in math, I majored in miracles. And I still believe in those, too," Mr Huckabee said.
President George Bush said yesterday that Mr McCain still had "some work to do" among conservative Republicans but he praised the Arizona senator as a true conservative and promised to campaign for him. "I'd be glad to help him if he's the nominee - he is very strong on national defence, he is tough fiscally, he is pro-life. His principles are sound and solid," Mr Bush said.