WASHINGTON (AP) - Barack Obama's endorsement by John Edwards yielded immediate payoffs Thursday, as the Democrat picked up four of his former rival's 19 delegates and the backing of a powerful labor union as he appeared to speed toward his party's nomination.

Edwards' endorsement Wednesday came one day after his rival Hillary Rodham Clinton, riding strong support from her white, working-class, base routed Obama in the West Virginia primary. Though Obama's lead in delegates appears insurmountable, Clinton sought to use her victory to renew doubts about Obama's ability to win important industrial states in the November election against Republican John McCain.

But the announcement Thursday that the Steelworkers union was backing Obama offered him new hope of winning the support of crucial working class voters who have so far shunned him.

Edwards, a former North Carolina senator and 2004 vice presidential nominee, had cast his presidential bid on populist terms, supporting working class voters' causes in an election season dominated by concerns about the U.S.'s sagging economy.

And hours after Edwards said he was backing the Illinois senator some of his delegates followed suit, adding to Obama's growing lead in delegates needed to win the nomination. Obama is now just 135 delegates shy of the number needed to clinch.

Clinton also has adopted a populist platform, portraying herself as the candidate best equipped to deal with the country's housing and credit crisis while depicting Obama as a political novice long on gilded promises but short on feasible solutions.

Despite her push, Democrats have increasingly lined up behind the first-term Illinois senator - with Edwards being among the most prominent.

Edwards made a surprise appearance with Obama in Michigan, a general election battleground state that was stripped of its delegates for holding its Democratic primary early. It is also in an industrial state which has had the U.S.'s highest jobless rate for much of the past few years.

Edwards said Obama "stands with me" in a fight to cut poverty in half within 10 years.

Clinton, meanwhile has vowed to continue her heavily indebted campaign, despite concerns that the protracted and, at times, acrimonious race could undercut the Democrats' chances of recapturing the White House this year.

Her supporters played down Edwards' endorsement.

"I think it certainly helps in terms of the psychology of the superdelegates," Political strategist and Clinton ally James Carville told ABC's "Good Morning America" on Thursday. But he cast doubts that it would sway many voters.

Superdelegates are party officials who can vote as they please at the presidential nominating convention. Clinton's scant hopes are based on the possibility that an overwhelming number of superdelegates will back her.

With only five contests remaining, Clinton has no real hope of overtaking Obama through primary wins: the fresh support brought Obama's overall delegate total to 1,892, compared to 1718 for Clinton. It takes 2,026 to clinch the nomination at the party convention in Denver this summer.

Obama has turned his focus away from Clinton and looked toward a November election battle against McCain. He has sought to cast McCain as a continuation of President George W. Bush's unpopular presidency, at a time Americans are worried about the weak economy and the Iraq war.

On Thursday, Obama took aim at Bush, accusing him of launching a "false political attack" with a comment before the Israeli Knesset about appeasing dictators.

Obama's campaign interpreted the remark as a slam against the candidate's earlier suggestion that he would, as president, negotiate directly with Iran and groups hostile to the United States.

"George Bush knows that I have never supported engagement with terrorists, and the president's extraordinary politicization of foreign policy and the politics of fear do nothing to secure the American people or our stalwart ally Israel," Obama said in a statement.

The White House denied the remark, which Bush made during a speech as Israel celebrates its 60th birthday, was aimed at Obama.

McCain, meanwhile, made predictions about the end of his first term in 2013 during a speech Thursday in Ohio in which he implicitly suggesting he would seek a second term. That is an attempt to mute suggestions the 71-year-old would serve only four years after being the oldest president ever to take office for a first term.

In particular, McCain said he sees a world in which:

- "The Iraq war has been won. Iraq is a functioning democracy, although still suffering from the lingering effects of decades of tyranny and centuries of sectarian tension. Violence still occurs, but it is spasmodic and much reduced."

- The Taliban threat in Afghanistan has been greatly reduced.

- "The increase in actionable intelligence that the counterinsurgency produced led to the capture or death of Osama bin Laden, and his chief lieutenants."

- A "League of Democracies" has supplanted a failed United Nations to apply sanctions to the Sudanese government and halt genocide in Darfur.

- The United States has had "several years of robust growth."