Obama, McCain Sweep Potomac Primaries

On a primary winning streak, Sen. Barack Obama, D-Ill., swept the so-called Potomac primaries last night, overwhelmingly defeating Sen. Hillary Clinton, D-N.Y., in Democratic contests in Maryland, Virginia and Washington, D.C.

For the first time, the Illinois senator has taken the lead over Clinton in the ABC News overall delegate estimate.

This is the eighth straight victory for Obama, who is increasingly taking on the mantle of Democratic frontrunner.

"Today, the change we seek swept through the Chesapeake and over the Potomac. We won the state of Maryland. We won the Commonwealth of Virginia. And though we won in Washington D.C., this movement won't stop until there's change in Washington," Obama told supporters at a rally in Madison, Wisc. last night.

"We are bringing together Democrats and Independents and Republicans; blacks and whites; Latinos and Asians; small states and big states; Red States and Blue States into a United States of America," Obama said. "This is the new American majority."

On the Republican side, Sen. John McCain, R-Ariz, won primaries in Maryland and Washington, D.C. and battled back insurgent candidate Mike Huckabee, the former Arkansas governor, in a Virginia primary made close by a high turnout of conservatives and Christian evangelicals.

"He certainly keeps things interesting, a little too interesting at times tonight," McCain said of Huckabee at a campaign rally in Alexandria, Va. "Makes it more interesting."

Clinton's Potomac Defeat

Clinton's defeat in the Virginia primary crushed what may have been her best chance at a Potomac primary win.

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Clinton had hoped to perform strongly in Virginia's rural communities and among women and the state's sizeable Hispanic and immigrant population, but Obama ultimately prevailed in the state, winning demographic groups once thought to be Clinton's core.

Ignoring her losses and her Democratic rival, Clinton addressed a campaign rally in El Paso, Texas -- one of the states she is focusing her campaign on winning March 4.

"I need you to stand up for me because, because if we stand up together, if we work together, if we fight together, we will take back America and we will make history together," Clinton said.

In a sign of further turmoil within Clinton's campaign, word came late tonight that Clinton's deputy campaign manager Mike Henry stepped down today, reports ABC News Kate Snow.

Henry is famous for a leaked memo he wrote suggesting that Clinton skip Iowa. He was loyal to former campaign manager Patti Solis Doyle, who was replaced two days ago.

Obama Swept to Victories

Obama swept to victories in Virginia, Maryland and D.C.where majorities of Democratic voters said the top attribute they are seeking in a candidate is the one who can "bring needed change," according to preliminary exit poll results -- a message consistently promoted by Obama.

Obama won 88 and 89 percent of African-American voters in Virginia and Maryland and rode majority support from white men.

White voters in Virginia favoring him over Clinton by a 14-point margin, according to preliminary exit results reported by ABC News' Gary Langer.

Obama was also helped by independents, who made up a fifth of voters in Virginia's open primary.

McCain Beats Back Huckabee

McCain, who is trying to court conservatives unhappy with his record on taxes, immigration and his opposition to a federal ban on same-sex marriage, battled back Huckabee in Virginia, where a high turnout of Christian evangelicals and conservatives made it a tight race.