With a clean sweep in the so-called "Potomac Primaries" on Tuesday night, Senator Barack Obama brought his winning streak to eight in a row against Democratic presidential rival Senator Hillary Clinton. But more important, the elections gave Obama the lead in delegates in his neck-and-neck race with Clinton. Senator John McCain also pulled off a sweep in the three Republican primaries, virtually eliminating any possibility that former Arkansas Governor Mike Huckabee could put up a legitimate fight for the nomination.

What is notable about Obama's wide-margin wins in the District of Columbia, Maryland and Virginia is that exit polls show he drew support not only from the groups that have already been backing him — black voters, young people, independents and those with high incomes — but also among groups that have been Clinton's core constituency, including older voters, women and lower-income people, according to The New York Times. In Washington, Obama took 75 percent of the vote to Clinton's 24 percent. In Maryland, he had 60 percent to her 27 percent, and in Virginia, he had 64 percent to her 35.

Though Huckabee, a former Baptist minister, got support from conservative and evangelical Christian voters in Virginia, McCain still took 50 percent of the vote in that state to Huckabee's 41 percent. The senator had 68 percent in the District of Columbia to Huckabee's 17 percent, and 55 percent in Maryland to Huckabee's 29 percent. All three were winner-take-all contests, netting him 89 additional delegates. Huckabee has repeatedly vowed to stay in the race, despite the fact that even if he wins all the remaining races by pulling 60 percent of the vote in each one, he would still not be able to win the nomination. "He certainly keeps things interesting — maybe a little too interesting at times tonight, I must confess," McCain said after his victories, according to the Times.

Obama's lead in the delegate count comes at a time when the Clinton campaign has been struggling, following the resignation on Tuesday of deputy campaign manager Mike Henry and last week's demotion of campaign manager Patti Doyle. Clinton did not campaign heavily in the Potomac states, essentially conceding that Obama would win those contests. Instead, she has been concentrating on the delegate-rich March 4 primaries in Ohio and Texas.

While Obama again won nearly 90 percent of the black vote in Tuesday's contests, in another potentially troubling sign for Clinton — who did not congratulate Obama on his victories on Tuesday — he has begun to cut into her lead among Latino voters as well, according to exit polls. The polls show he also gained ground among white men, winning a majority in both Virginia and Maryland.

According to CBS News estimates, the Democratic delegate count now stands at 1,242 for Obama and 1,175 for Clinton, with 2,025 needed to secure the nomination.

Obama reveled in his front-runner status during a rally in Madison, Wisconsin, Tuesday night, already looking forward to next Tuesday's contests in that state and Hawaii (where he lived as a child). "We also know that, at this moment, the cynics can no longer say our hope is false," he said. "We have now won east and west, north and south, and across the heartland of this country we love."

Obama also seemed to turn his attention to the general election, telling the crowd, "John McCain, the likely Republican nominee, is an American hero. And we honor his service to our nation. ... But his priorities don't address the real problems of the American people, because they are bound to the failed policies of the past."

Not to be outdone, McCain lobbed his own warnings about Obama at a rally in Alexandria, Virginia, the Times reported. "To encourage a country with only rhetoric rather than sound and proven ideas that trust in the strength and courage of free people is not a promise of hope. ... It is a platitude," McCain said, adding a bit of Obama's signature campaign line for emphasis, "My friends ... I promise you, I am fired up and ready to go." McCain leads Huckabee in the delegate count 790 to 199, according to CBS News estimates, with 1,191 needed to clinch the Republican nomination.

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