Denver (AP)  -- Barack Obama stands before delegates and the nation Thursday -- the 45th anniversary of Martin Luther King Jr.'s historic "I Have a Dream" speech -- to accept the Democratic presidential nomination, the first black man to claim such a prize.

The drama of his long, emotional primary struggle against Hillary Rodham Clinton behind him at last, Obama's long-awaited convention speech will propel him into a tough sprint to Election Day, a mere nine weeks away.

Listen to MA State Senate President Therese Murray, Gov. Deval Patrick, Sen. Hillary Clinton and House Speaker Nancy Pelosi.

Obama's march into history will be coupled with a modern-day technological effort to get most of the 75,000 packed into Invesco Field at Mile High stadium to form the world's largest phone bank -- text-messaging thousands more to boost voter registration for the fall.

Any edge is imperative as polls show a close race between Obama and Republican presidential candidate John McCain in the bid to become the nation's 44th president, succeeding George W. Bush.

Obama accepts his party's nod on a day few could ever imagine decades ago, when King fought for civil rights.

"This is a monumental moment in our nation's history," Martin Luther King III, the civil rights icon's oldest son, told The Associated Press on Wednesday. "And it becomes obviously an even greater moment in November if he's elected."

Obama was just 2 years old when King addressed a sea of people on the National Mall in Washington on Aug. 28, 1963. The civil rights leader proclaimed on the steps of the Lincoln Memorial, "I have a dream, that one day this nation will rise up and live out the true meaning of its creed -- 'We hold these truths to be self-evident: that all men are created equal."'

Obama, known for his stirring oratory, has been trying to lower expectations for his acceptance speech. Senior strategist David Axelrod said Obama would lay out a case for sweeping political change and illustrate the choice voters face between his candidacy and that of McCain.

"His goal is to talk to the American people about the challenges we face and what we need to do to solve them, and the stakes of continuing to do what we are doing," Axelrod said. "I will leave it to others to decide the inspiration factor."

Adding a touch of celebrity to the convention's final night, singers Sheryl Crow, Stevie Wonder and will.i.am were scheduled to perform, with Academy Award-winner Jennifer Hudson singing the national anthem.

After days of suspense over whether Clinton supporters would fall in line behind Obama when the roll call of the states was called, it all fell into place in the end for Obama.

Delegates in dozens of states were allowed to apportion their votes between Obama and the former first lady before Clinton herself stepped forward to propose that Obama be declared the nominee by acclamation.

Obama himself paid a late-night visit to the Pepsi Center, home for the first three nights of the convention, where 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."

Former President Clinton did his part to bring about unity too, delivering a strong pitch for the man who outmaneuvered his wife for the nomination, and going through a litany of GOP policies the former president said were hurting the country.

"My fellow Democrats, America can do better than that. And Barack Obama will do better than that," Clinton said.

Clinton and Delaware Sen. Joe Biden, who accepted the vice presidential nomination by acclamation Wednesday night, brought Democratic jabs at McCain and President Bush into prime time as Democrats sharpened their attacks after two days of largely feel-good rhetoric.

"These times require more than a good soldier. They require a wise leader," Biden said. "A leader who can change ... the change that everybody knows we need."

Biden's attacks on McCain were a big hit among delegates eager to put aside their intraparty squabble so they can start going after Republicans.

The reconciliation was taking place, delegate by delegate.

"I was a Clinton delegate," said Darlene Ewing, a delegate from Texas. "I'm an Obama person now."

On Thursday, former Vice President Al Gore will add his voice to the lineup of Democratic luminaries trying to motivate party members for the fall.