The fresh support brought Obama's overall delegate total to 1,888, compared to 1,711 for his rival, latest CBS News tally. It takes 2,025 to clinch the nomination at the party convention in Denver this summer., according to the
Edwards, who bestowed his long-sought endorsement on Obama on Wednesday, won 19 delegates before departing the presidential race in January.
Within hours, Obama picked up the backing of three of them from South Carolina and one in New Hampshire.
In addition, three superdelegates - Reps. James McDermott of Washington, and Henry Waxman and Howard Berman of California - endorsed Obama.
"I believe now is the time to unite behind Barack Obama so we can be in the strongest place possible to win in November," McDermott said.
Waxman said in a statement: "I have the greatest respect and admiration for Senator Clinton and former President Clinton ... It is now clear, however, that the Democratic Party is nearing a broad consensus on our nominee."
Edwards had been backed by the United Steelworkers Union, which announced it would now support Obama. The union has 600,000 active members, many of them blue-collar workers of the type that have favored Clinton in recent primaries.
Obama also picked up the personal endorsement of superdelegate Larry Cohen, the president of the Communication Workers of America union.
"Senator Obama is uniquely positioned to broaden the Democratic party base and lead the party to election gains at every level this year as well as reclaiming the White House," said Cohen, who lives in the nation's capital.
The increased support came despite Obama's overwhelming defeat in Tuesday's primary in West Virginia, and suggested that Clinton's argument that she would be a better general election candidate was not finding a receptive audience.
The former first lady is favored to win next week's primary in Kentucky, while Obama is expected to win in Oregon the same day.
The delegates won by Edwards are not bound by his endorsement of Obama, but several said it is important to their decision.
"I will cast my vote for who John Edwards asks me to," said Robert Groce, a South Carolina delegate won by Edwards.
Iowa delegate Dave Redlawsk said he was not ready to declare for Obama. But, he added, "John's endorsement weighs heavily in a positive way. I take seriously his endorsement, his recommendation in a sense."
With the primary season winding down, both Clinton and Obama have turned their attention increasingly to the superdelegates, the members of Congress and other party officials who have seats at the convention by virtue of their positions.
Obama long trailed Clinton among superdelegates, but overtook her last week, and has pulled further away despite suffering one of his worst defeats in the campaign in West Virginia.
Clinton spent the day campaigning in South Dakota, one of two states that closes out the primary season on June 3. Obama was home in Chicago.
Both rivals had avidly sought Edwards' endorsement, particularly in the weeks after he dropped out of the race. The former North Carolina senator and 2004 vice presidential nominee had campaigned as a champion of the working class, and in the wake of his departure, Clinton consistently drew more blue-collar votes than Obama did.
"We are here tonight because the Democratic voters have made their choice, and so have I," Edwards said Wednesday to thunderous applause from an audience in Grand Rapids, Mich. He said Obama "stands with me" in a fight to cut poverty in half within 10 years, a claim Obama confirmed moments later.
Edwards told the rally that "we must come together as Democrats" to defeat Republicanin November.
He also praised Clinton.
"We are a stronger party" because of her involvement and "we're going to have a stronger nominee in the fall because of her work," he said.
Then as Edwards sat on stage and watched, Obama gave one of his most animated addresses in days, much of it devoted to fighting poverty. In America, he said, "you should never be homeless, you should never be hungry."
Clinton campaign chairman Terry McAuliffe said in a statement: "We respect John Edwards, but as the voters of West Virginia showed last night, this thing is far from over."
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