Denver — Democrats formally named Barack Obama their presidential candidate Wednesday, putting their hopes of ending eight years of Republican control of the White House in the hands of a man who would be the United States' first black president.

Former rival Hillary Rodham Clinton interrupted a state-by-state roll call vote at the Democratic National Convention to ask delegates to make Obama's selection unanimous "in the spirit of unity, with the goal of victory." They agreed, with a roar.

Hours later, her husband added his backing. Former President Bill Clinton, whose past support for Obama has been tepid, told delegates and a national television audience that Obama "is ready to lead America and restore American leadership in the world."

Though the convention vote offered no surprises, its historical importance was undeniable. It capped the longest, closest U.S. primary race in memory as Obama, a 47-year-old political newcomer, defeated Clinton, the former first lady whose victory once seemed all but assured.

It also meant that Obama, the son of a black Kenyan father and a white American mother, is now one victory from becoming president of a nation where, just decades ago, many blacks were denied the vote.

Obama was across town as the delegates he won in months of primaries sealed his victory. He briefly made an unscripted appearance at the end of Wednesday's session, joining Sen. Joe Biden on stage after Biden accepted the party's vice presidential nomination.

"I think the convention's gone pretty well so far, what do you think?" he said as the crowd thundered its approval.

Obama's formal acceptance speech Thursday night was expected to draw a crowd of 75,000 at a nearby outdoor stadium.

Obama's prospects in the Nov. 4 election are uncertain. He is in a tight race with Republican John McCain, a veteran senator and former prisoner of war in Vietnam, who has attacked Obama for his lack of experience. Obama has had to fend off questions about his patriotism and rumors that he is a Muslim. No one knows how many Americans simply will not vote for a black candidate.

The first-term Illinois senator also needs to unite a party fractured by the long and bitter primary campaign. That process received a boost Tuesday with an enthusiastic speech by Clinton, who said Obama is "my candidate, and he must be our president."

Bill Clinton echoed his wife's words. Noting that she had told the convention she would do everything possible to get Obama elected, he said: "That makes two of us."

For months, the former president had made little secret of his disappointment over his wife's primary defeat. During her campaign, he faced criticism for his outbursts of anger and deprecatory comments about Obama.

But his 1993-2001 presidency is warmly remembered by Democrats as a time of peace and prosperity. He was greeted with a long, huge ovation and interrupted with applause as he lauded Obama.

"Everything I've learned in my eight years as president and the work I've done since, in America and across the globe, has convinced me that Barack Obama is the man for this job," he said.

The difficulty in uniting the Clinton and Obama camps showed in the careful negotiations for the delegate roll-call that sealed Obama's nomination. Clinton, who won nearly 18 million votes and but could not overcome Obama's delegate total, had wanted the pro forma roll call as a cathartic moment for her huge bloc of supporters.

The compromise, that allowed her to be nominated and the votes to be counted through a partial roll call of states, provided a middle ground and a hope for united Democratic front.

Less than an hour before the roll call, Clinton began an emotional gathering with her delegates by telling them she had released them to vote for Barack Obama. Many in the crowded ballroom yelled back "No!"

Despite releasing her delegates, Clinton received 341 votes, to Obama's 1,549, before she called for him to be approved by acclamation.

Tensions between the two camps were aggravated last week by Obama's decision to name Biden instead of Clinton as his vice presidential running mate. But in their speeches, both Clintons commended the choice.

Biden received the nomination by acclamation Wednesday night. In his acceptance speech, he praised Obama as the leader the United States needs during tough economic times. He said he learned the quality of Obama's character while campaigning against him for the presidential nomination.

"I watched how Barack touched people, how he inspired them, and I realized he had tapped into the oldest American belief of all: We don't have to accept a situation we cannot bear. We have the power to change it," he said.

Obama has campaigned on a theme of hope and change, tapping into voter dissatisfaction with the old politics of Washington and the unpopular presidency of Republican George W. Bush.

He was little known outside his home state of Illinois until 2004 when, as a candidate for the Senate, he dazzled with a keynote address at the Democratic National Convention. He won election to the Senate, then announced his presidential candidacy a scant two years after arriving in Washington.

With his gifts as a speaker, his astounding ability to raise money on the Internet and an unmatched ground operation pieced together by political veterans, he won a stunning victory in the first nominating contest, the Iowa caucuses on Jan. 3.

Obama has pledged to pull U.S. combat forces out of Iraq in 16 months and to make health care available to all Americans.

He has called for bipartisan unity and targeted western and southern states that have been Republican strongholds. But he is vulnerable in northern industrial states, Clinton strongholds that have been crucial to Democratic hopes. Obama, his wife, Michelle, and Biden and his wife, Jill, will embark on a bus tour of three of those states: Pennsylvania, Ohio and Michigan.

Republicans hold their convention next week to anoint McCain as their candidate. He has not yet announced a running mate, but was expected to do so soon.

On Wednesday, McCain's campaign released a new TV ad saying that Obama showed he was "dangerously unprepared" for the White House when he described Iran as a "tiny" nation that did not pose a serious threat.

Missing from the ad was the context of Obama's remarks last May in which he compared Iran and other U.S. adversaries to the superpower Soviet Union.

In his speech, Bill Clinton defended Obama's national security credentials. Recalling that when he ran for president at age 46 in 1992, "Republicans said I was too young and too inexperienced to be president."

"Sound familiar?" Clinton said. "It didn't work in 1992, because we were on the right side of history. And it won't work in 2008, because Barack Obama is on the right side of history."



Copyright 2008 The Associated Press.