(CBS/AP) Democrat Barack Obama swept Tuesday's "Potomac Primary", defeating Hillary Clinton in Virginia, Maryland and the District of Columbia, all by double-digit margins.
The two states and the District were also friendly territory for John McCain, who defeated Mike Huckabee in Republican contests.
With nearly all the Virginia Democratic vote in, Obama led Clinton, 64 percent to 35 percent. McCain's margin was smaller -- with nearly all precincts reporting, he led Huckabee, 50 percent to 41 percent.
McCain's won Virginia by performing extremely well in the state's Washington, D.C., suburbs -- in Fairfax County, for example, he won 64 percent of the vote, his best countywide result in the state. His margins there offset Huckabee's wins in the state's more rural counties, particularly in southwest Virginia.
Obama's victory there followed a pattern similar to McCain's, with him winning nearly every county in eastern and central Virginia.
In the District of Columbia -- where the Democratic electorate is comprised largely of African-Americans and affluent whites -- Obama crushed Clinton, winning 75 percent of the vote compared to Clinton's 24 percent. Turnout in that contest was 20 times that of the Republican primary, which McCain won handily with 68 percent of the vote.
Returns from Maryland trickled in slowly, but with 92 percent of the votes counted Obama was ahead of Clinton, 60 percent to 37 percent. Obama performed especially well in Baltimore, the Eastern Shore counties, and suburbs of both Baltimore and Washington, D.C., while Clinton carried outlying northern counties.
The outcome in Maryland was delayed when a judge ordered voting hours extended 90 minutes to 9:30 p.m. because of inclement weather and associated traffic problems.
"Clinton's seawall has broken down, bit by bit, contest by contest with the relentless waves of support for Obama, slowly eroding barriers once believed to be impenetrable and one that threatens to break down even more," CBSNews.com senior political Vaughn Ververs said. "In the first-ever Potomac Primary, the wave crashed through Clinton's wall."
McCain was well ahead of Huckabee in Maryland, with 55 percent of the vote to Huckabee's 31 percent. McCain also appeared to carry all of the state's counties.
By prevailing in all three contests, Obama extends his post-Super Tuesday winning streak. Over the weekend, he beat Clinton by wide margins in Louisiana, Nebraska, Washington state, the Virgin Islands and Maine.
"The change we seek swept through the Chesapeake and over the Potomac," Obama said while speaking to a large crowd of supporters in Madison, Wis. "Though we won in Washington, D.C., this movement won't stop until there's change in Washington, D.C., and tonight we're on our way."
CBS News exit polls indicate that while Obama performed extremely well among African-American voters in both states -- he won 84 percent in Maryland and 90 percent in Virginia - he won the white vote in Virginia and, in both states, won among women, who in previous contests have usually favored the former first lady. Obama won 60 percent of women voters Virginia and 55 percent in Maryland. In Virginia's open primary, he dominated among independent voters, 69 percent of whom voted for the Illinois senator.
The results came as Clinton's campaign faced more staff changes. CBS News reports that deputy campaign manager Mike Henry has resigned, with no replacement yet named. On Sunday, Clinton's campaign manager, Patti Solis Doyle, was replaced by longtime aide Maggie Williams.
Despite the results and continuing changes in her campaign staff, Clinton sounded an upbeat note in speaking to supporters in El Paso, Texas.
"We're going to sweep across Texas in the next three weeks, bringing out message about what we need in America, the kind of president that will be required on Day One to be commander in chief to turn this economy around," she said. "I'm tested, I'm ready -- let's make it happen."
Both candidates' decision of where to speak Tuesday night said volumes about their strategies going forward. Obama's campaign hopes the night's wins, followed by victories next Tuesday in Wisconsin and Hawaii, will give him enough momentum and delegates to establish him as a clear front-runner in the eyes of voters and superdelegates -- the elected officials and party leaders who have votes at the party's convention and can change their mind at any time. Clinton has placed her hopes for stopping Obama in the March 4 primaries in Ohio and Texas, two large states that are demographically more favorable to her candidacy.
Aides to the former first lady concede she is in the midst of a difficult period in which she could lose 10 straight contests. She is hoping to rebound on March 4, in primaries in Ohio and Texas, states where both candidates have already begun television advertising.
Obama has campaigned before huge crowds in recent days, and far outspent his rival on television advertising in the states participating in the regional primary. He began airing commercials in the region more than a week ago, and spent an estimated $1.4 million. Clinton began hers last Friday, at a cost estimated at $210,000.
Obama's wins Tuesday allowed him to extend his narrow lead over Clinton in the all-important race for delegates to the party's national convention. According to delegate estimates compiled by CBS News Obama has 1,242 delegates while Clinton has 1,175. Subtracting superdelegates who have endorsed or indicated support for either candidate, Obama leads Clinton, 1,101 to 965. A candidate needs 2,025 delegates to secure the nomination.
The economy continued to be the dominant issue in Democratic voters' minds, according to early CBS News exit polls conducted in Maryland and Virginia. In both states, nearly half of those voting in Democratic primaries said the economy was their top concern, while 30 percent cited the war in Iraq. Nine of 10 voters said the economy was in bad shape.
In both states, more than half of Democratic voters said the ability to bring change was the most important quality they looked for in a candidate -- in Maryland the number was 56 percent, compared to 57 percent in Virginia.
Democrats in Maryland and Virginia had nearly identical opinions on the questions of who was more likely to unite the country and who would make a better commander in chief. The exit polls in both states found that more than two-thirds of voters believed Obama was more likely to unify the country and at least half felt he was most qualified to be commander in chief.
In the Republican race, McCain further expanded his already wide lead in the delegate count. He won all the delegates available in Virginia and the District -- Republican Party rules allow for the allocation of delegates on a "winner take all" basis. CBS News estimates McCain has won 790 delegates so far, giving him two-thirds of the 1,191 required to secure the nomination. Huckabee, a former Arkansas governor, is far behind, with 199 delegates.
His nomination all but assured, McCain focused on the general election in remarks delivered to supporters in Alexandria, Va. Reflecting the current trend in the Democratic contest, he seemed to single out Obama, known for his soaring oratory and emphasis on hope.
"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," McCain said. "It is a platitude."
Among Republicans, McCain appeared to rebound from a poor weekend showing. McCain lost caucuses in Kansas and a primary in Louisiana on Saturday to Huckabee, his last remaining major rival. He won caucuses in Washington state.
Exit polls indicated McCain still hadn't convinced many voters of his conservative credentials: 49 percent in Virginia, and 41 percent in Maryland, said McCain isn't conservative enough. Yet 77 percent in both states said they were satisfied to have him as the party's nominee. While majorities of frequent talk radio listeners and self-identified conservatives favored Huckabee in Virginia, McCain won among them in Maryland.
Shared values were cited as the most important quality in a candidate in both Maryland (40 percent) and Virginia (45 percent). Evangelical Christians formed a somewhat higher percentage of the Republican primary vote in Virginia (46 percent) than in Maryland (34 percent).
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