DENVER (AP) -- Barack Obama swept to the Democratic presidential nomination Wednesday night, a transforming triumph that made him the first black American to lead a major party into the fall campaign for the White House.

Former President Clinton did his part to bring about unity, delivering a strong pitch for the man who defeated his wife for the nomination.

After Biden's acceptance speech, Obama himself paid a late-night visit to the Pepsi Center, home for the first three nights of the convention. He embraced Biden and implored the delegates to help him "take back America" in the fall campaign.

"Change in America doesn't start from the top down," he told the adoring crowd, "it starts from the bottom up."

Obama's formal acceptance speech Thursday night was expected to draw a crowd of 75,000 at a nearby football stadium where an elaborate backdrop was under construction.

Obama, 47 and in his first Senate term, carries the Democrats' hopes of recapturing the White House into the fall campaign against Sen. John McCain and the Republicans.

Inside the convention hall, the outcome of the traditional roll call of the states was never in doubt, only its mechanics.

"No matter where we stood at the beginning of this campaign, Democrats stand together today," declared Rep. Debbie Wasserman Schultz of Florida, a former Clinton supporter who delivered a nominating speech for Obama.

"We believe passionately in Barack Obama's message of changing the direction of our country," she said.

Earlier in the day, Clinton formally released her delegates amid shouts of "no," by disappointed supporters. "She doesn't have the right to release us," said Massachusetts delegate Nancy Saboori. "We're not little kids to be told what to do in a half-hour."

She was warmly embraced by delegates split between herself and Barack Obama in the primary. Any who were still angry over her loss were drowned out in applause when she opened her speech by declaring herself "a proud supporter of Barack Obama."

She exhorted her backers -- "my sisterhood of the traveling pantsuits," she called them -- to remember who was most important in this campaign.

"I want you to ask yourselves: Were you in this campaign just for me?" she said. She urged them instead to remember Marines who have served their country, single mothers, families barely getting by on minimum wage and other struggling Americans.

"You haven't worked so hard over the last 18 months, or endured the last eight years, to suffer through more failed leadership," Clinton told the delegates. "No way. No how. No McCain."

The line drew applause from Obama, who was watching on television from Billings, Mont., with supporters and reporters.

AP Photo

Sen. Barack Obama watches Sen. Hillary Clinton's speech at the Democratic National Convention on August 26, 2008.

Clinton spoke on the eve of the delegate roll call in which both she and Obama will be nominated for president. But under a deal between the two camps, only some delegates will get the opportunity to cast a historic vote for either a woman or a black man before the split decision will be cut off in favor of unanimous consent for Obama.

More: Ore. delegate blogs from DNC

Advisers to Clinton and Obama sent a joint letter Tuesday night instructing state delegation chairs to distribute vote tally sheets to delegates Wednesday and return them by 4 p.m. local time, just as the vote is scheduled to get under way.

The letter said Clinton would have one nominating speech and two seconding speeches, followed by Obama's nominating speech and three seconding speeches -- totaling no more than 15 minutes for each candidate. Then the roll call will begin, said the letter signed by Obama senior adviser Jeff Berman, Clinton senior adviser Craig Smith and convention secretary Alice Germond.

The dealmaking and lack of direction left Clinton supporters frustrated. Clinton fueled confusion by refusing to publicly instruct her delegates how to vote, though she said she'll back Obama when the time comes. She planned to meet with her delegates Wednesday.

All the Clintons, a longtime royal family of Democratic politics, were on hand to pass the torch to Obama. Clinton was introduced by her daughter Chelsea, while her husband watched from a box seat above the Arkansas delegation. Not everyone with a ticket could get in to hear Clinton after fire marshals declared the hall filled to capacity.

The convention hall was brimming with delegates wearing Clinton gear. There were Hillary T-shirts, buttons and stickers. Some delegates brought signs promoting Clinton for president. Many wore white shirts to mark the 88th anniversary of women's suffrage.

"My mother was born before women could vote," Clinton reminded them. "But in this election my daughter got to vote for her mother for president."

The Obama campaign gave Clinton her due. Before she took the stage Tuesday night, Obama's campaign distributed "Hillary" signs throughout the Pepsi Center. But only sentences into Clinton's speech, those signs were quickly swapped out for others proclaiming either "Obama" or "Hillary" on one side, and "Unity" on the other.

Some Clinton delegates weren't ready for so quick a pivot.

"We love you Hillary!" some shouted.

Jennie Lou Leeder, a Clinton delegate from Llado, Texas, said Clinton "was so good tonight, I was crying."

Did her speech help to unify the party?

"It's not Hillary's job to bring this party together," Leeder said. "It's Barack Obama's job to bring this party together."

Daniel Kagan, a Clinton delegate from Englewood, Colo., said he felt pride and sadness watching Clinton speak. He was proud of her accomplishments, but saddened by the realization that her campaign was truly over.

Nevertheless, Kagan said, the speech will help to unify the party.

"I know that it's changed attitudes," Kagan said. "I saw some of my colleagues standing up and applauding for Obama for the first time."

It was the culmination of an emotional day for Clinton loyalists, still wondering how the final act would play out in Wednesday's roll call vote and whether they would have a chance to give their candidate one last show of support.

Party leaders said they feared a nationally televised floor demonstration Wednesday that would underscore party divisions.

"It seems to be a little more of a problem than I anticipated," former Democratic Party chairman Don Fowler told the AP. "All you need is 200 people in that crowd to boo and stuff like that and it will be replayed 900 times. And that's not what you want out of this."