Obama looks to sweep Maryland, Virginia, Washington primaries

Democrat Barack Obama hoped to extend his winning streak as voting began on Tuesday in three presidential primary battles, while rival Hillary Rodham Clinton focused on future spoils amid expectations that the day's races were already lost.

Obama seemed to be coasting into Tuesday's so-called Potomac primary contests in Washington, DC, Virginia and Maryland, after he overwhelmingly won five weekend contests. He was expected to be supported by black Democrats, a bloc that has aided his wins in earlier matchups against Clinton.

On the Republican side, John McCain hoped to rebound with three wins on the way to his likely nomination after embarrassing losses to Mike Huckabee in weekend contests showed he still had much to do to convince the party's core conservative blocs that he is one of them.

The Arizona senator lost in Kansas and Louisiana during the weekend, but managed a narrow win in Washington state caucuses that Huckabee, the former Arkansas governor, is now challenging.

In the Potomac primaries, 168 delegates are up for grabs in the Democratic race and Republicans are competing for 116.

Polls showed Obama with double-digit leads in both Maryland and Virginia, where Gov Tim Kaine campaigned at his side. The Illinois senator was counting on big wins to erase Clinton's slim delegate lead for an edge in a contest that could stretch to the Democrats' national convention in August.

He brushed aside questions today about future votes to which Clinton is turning her attention.

"It's very early," Obama said when asked about his prospects in the March 4 Texas primary. "We haven't even gotten through this yet.