Maryland, Virginia and the District of Columbia usually hold primaries after the two parties' nominees are settled. This year, however, the Democratic nomination remains very much in play - and the Republican contest still has life - as the contests move to the mid-Atlantic region.
What some have dubbed the Potomac Primary "could be pivotal," said Peter Franchot, a Democrat elected as Maryland's comptroller in 2006.
Most of the action is on the Democratic side. Sens.and are battling over 168 delegates in heavily Democratic Maryland and D.C., and in Virginia, once a reliably Republican state in presidential elections but now a more competitive prize.
Republicans have 116 delegates at stake that day, but virtually no campaigning has taken place so far. "There's not much going on" in Virginia, Sen. John Warner, R-Va., said Tuesday, although he is trying to stir up support for fellow Sen.of Arizona.
Handicapping the Feb. 12 races is difficult. With the 24-state Super Tuesday election consuming nearly all the candidates' time and money until now, campaign activities and reliable polling have been scarce.
In fact, people showed up at polling places across Virginia on Tuesday, thinking their state was part of the Super Tuesday hoopla rather than one of those voting a week later. Election officials in Maryland and the District of Columbia also reported phone calls from confused voters.
Political activists say Obama should do well in the District of Columbia, a predominantly black city with 15 pledged delegates. D.C. Mayor Adrian M. Fenty endorsed him months ago.
Maryland also is well-suited to the Illinois senator, party insiders say, while Virginia is more of a toss-up.
Virginians do not register by party, which allows independents to vote in either primary. That might help Obama, but it complicates all campaigns' efforts to target and predict likely voters, especially among newcomers.
Maryland has two large blocs of voters - African-Americans and affluent white liberals - who have flocked to Obama in other states. Black voters are concentrated in Baltimore and the large Washington suburb of Prince George's County.
Highly educated, upper-income whites are especially prevalent in another major Washington suburb, Montgomery County, which includes Bethesda, Silver Spring and Rockville.
"It's hard to see how Hillary Clinton finds the foundation" for a big vote in the remaining counties, said Keith Haller, a Maryland-based pollster who is not involved in the presidential race. "You've got the portents for Maryland being one of Obama's best states," he said.
Clinton is hardly conceding Maryland, however. Her endorsers include Gov. Martin O'Malley, Sen. Barbara Mikulski and Prince George's County Executive Jack Johnson, who is black.
"We feel very strong about the kind of support we've got everywhere" in the Feb. 12 states, said Clinton campaign spokesman Mo Elleithee.
Franchot, an Obama supporter, predicts that the Illinois senator's appeal to liberals and blacks will overwhelm Clinton's support from traditional party leaders. "It's the reform wing of the party, plus African-Americans," he said, "against the establishment."
In Virginia, Obama and Clinton will compete for 83 delegates mainly in the populous and fast-growing Washington suburbs, which include Fairfax County.
Obama should do well in the Richmond and Norfolk areas, which include sizable African-American communities. Clinton may prevail in more suburban and rural parts of the state, where her name recognition is strong and Obama has little time to make his case to voters who do not know him well.
Clinton planned to campaign Thursday in northern Virginia, and she said she will attend the annual Jefferson-Jackson Day Democratic fundraising dinner in Richmond on Saturday, a day when three other states - Washington, Louisiana and Nebraska - hold Democratic primaries. Those three states offer somewhat less prestige and fewer delegates than do the Washington-centric Feb. 12 states.
Clinton's Virginia endorsers include novelist John Grisham. But Obama has the support of Gov. Tim Kaine, seen by some as a rising star in the party.
In an interview Tuesday night, Kaine said "we're feeling pretty good" about Obama's chances in Virginia. Obama was the first to secure 10,000 signatures to get on the ballot, Kaine said, and he has "a really tested team" in the state.
The governor acknowledged, however, that "Senator Clinton has a lot of friends in Virginia."
In the GOP contest, the large number of active and retired military personnel in the Norfolk area should help McCain, a former Navy pilot and Vietnam War hero. Former Massachusetts Gov.and former Arkansas Gov. likely would split the state's social and religious conservatives.
"My gut is, Virginia is going to be a McCain state," said GOP Rep. Tom Davis, a veteran of northern Virginia politics and a McCain supporter.