Senator Barack Obama powered past Hillary Rodham Clinton in the race for Democratic convention delegates on a night of triumph sweetened with outsized primary victories in Maryland, Virginia and Washington, DC.

John McCain won all three Republican primaries on Tuesday, adding to his insurmountable lead in delegates for the Republican nomination.

''Tonight we're on our way,'' Obama told cheering supporters in Madison, Wisconsin, celebrating eight straight victories over Clinton, the former first lady is now struggling in a race she once commanded.

The Associated Press count of delegates showed Obama with 1,210. Clinton had 1,188, falling behind for the first time since the campaign began.

Neither was close to the 2,025 needed to win the nomination at the party's national convention this summer in Denver.

Obama's victories

Obama's victories were by large margins, he was gaining about 75 per cent of the vote in the nation's capital and nearly two-thirds in Virginia. He had 62 per cent of the vote in early Maryland returns.

By contrast, Clinton was attempting to retool her campaign in the midst of a losing streak. Her deputy campaign manager resigned, the second high-level departure in as many days.

Campaigning in Texas, where she hopes to triumph on March 4, she said she was looking ahead, not back.

''You know there is a great saying in Texas; you all have heard it. All hat and no cattle. Well, after seven years of George Bush, we need a lot less hat and a lot more cattle,'' she joked with supporters.

In all, there were 168 Democratic delegates at stake on Tuesday.

Obama moved past Clinton in the delegate chase on the basis of the day's primaries and newly released results from last Saturday's Washington state caucuses.

Democratic race

Additional delegates still to be allocated from his new victories were certain to add to his lead.

The Democratic race was the definition of unsettled, with Clinton surrendering her long-held lead in delegates, having shed her campaign manager and loaned her campaign $5 million in recent days, and facing defeats next Tuesday in Wisconsin and Obama's native Hawaii.

As the votes were counted in her latest setbacks, Clinton's deputy campaign manager stepped down.

Mike Henry announced his departure one day after Patti Solis Doyle was replaced as campaign manager with Maggie Williams, a longtime confidante of the former first lady.

Associated Press Online Video Editor Ron Fournier says Clinton's campaign ''is in trouble.''

''Hillary Clinton is in a boatload of trouble; she has now lost eight races in a row, Barack Obama has won more than two thirds of the states,'' said Fournier.

McCain's victory

McCain's victory in Virginia was a relatively close one, the result of an outpouring of religious conservatives who backed former Arkansas Governor Mike Huckabee.

Four in 10 Republican voters said they were born again or evangelical Christians, twice as many as called themselves members of the religious right in 2000, and nearly 70 per cent of them supported Huckabee, an ordained Baptist minister.

Virginia voters could vote in either primary in their state. In a twist, Huckabee was running slightly ahead of McCain among independents, who cast about a fifth of the Republican votes there.

There were 113 delegates at stake in the three Republican races.

The AP count showed McCain with 789 delegates. Former Massachusetts Governor Mitt Romney, who dropped out of the race last week, had 288. Huckabee had 241 and Texas Republican Ron Paul had 14.

It takes 1,191 delegates to clinch the Republican nomination at the party's convention in St Paul, Minnesota, and McCain appears to be on track to reach the target by late April.