Democratic presidential hopefuls Barack Obama and Hillary Rodham Clinton remain locked in tight battle ahead of the Potomac primary, with large pockets of black and highly educated voters.
A new USA Today/Gallup Poll shows Obama, who is vying to be America's first black president, edging ahead of the former first lady who wants to be the first woman chief executive, by 47 to 44 per cent after trailing her for a year.
The poll illustrated the fierce fight between the Democrats in the wake of the coast-to-coast Super Tuesday contests last week and ahead of this Tuesday's battle in the national capital of Washington and adjoining states of Virginia and Maryland.
Obama has been trying to make inroads among working-class voters with whom Clinton is strong. Clinton has also done better than Obama with Hispanic and Asian voters, both significant groups in Northern Virginia.
Robert Lang, co-director of the Metropolitan Institute at Virginia Tech, said Northern Virginia has so many immigrant groups that Hispanics and Asians may not be as helpful to Clinton. The area has a high concentration of people with college and postgraduate degrees, he said - a boon for Obama, who has done better with highly educated voters.
Obama also has an advantage in that blacks may be 40 per cent of the Democratic electorate, Lang said. Obama has drawn more than eight in 10 blacks in past contests.
Tom Schaller, a political scientist at the University of Maryland, Baltimore County, called Maryland "a home game for Obama". He said Clinton's support from seasoned Democratic politicians probably is "not enough to compensate for the huge lead Obama will have" among the state's liberal white voters and African-Americans, nearly a third of the population.
However, Clinton explained away Obama's clean sweep of the weekend's caucuses and primaries in four states as a product of a caucus system that favours "activists" and, in the case of the Louisiana primary, an energised African-American community.
"Everybody knew, you all knew, what the likely outcome of these recent contests were," she told reporters in Maryland on Monday.
"These are caucus states by and large, or in the case of Louisiana, you know, a very strong and very proud African-American electorate, which I totally respect and understand."
Clinton has publicly dismissed the caucus voting system since before Super Tuesday, seeking to lower expectations heading into a series of contests that played to Obama's advantage.
Noting that her husband, former president Bill Clinton, "never did well in caucus states either", Clinton argued that caucuses are "primarily dominated by activists" and that "they don't represent the electorate, we know that".
Clinton said she was "absolutely" looking forward to the Ohio and Texas primaries in March, where she believes voters are more receptive to her bread-and-butter message.
She also downplayed many of Obama's Super Tuesday victories, describing them as states that Democrats should not expect to win in November.
"It is highly unlikely we will win Alaska or North Dakota or Idaho or Nebraska," she said, naming several of Obama's wins in Republican dominated states. "But we have to win Massachusetts, New York, New Jersey, California, Arizona, New Mexico, Florida, Michigan... And we've got to be competitive in places like Texas, Missouri and Oklahoma."
Among Republicans, John McCain has consolidated his front-runner status, leading former Arkansas governor Mike Huckabee 53 to 27 per cent among Republicans and independents who "lean" Republican, according to USA Today/Gallup Poll.
Still, 51 per cent of Republicans say they are satisfied with McCain as the party's nominee, 45 per cent say they would have preferred another contender.
Even so, McCain remains competitive in head-to-head match ups against both Democratic contenders, beating Clinton by a single percentage point among likely voters and lagging Obama by four points - also within the margin of error.