DENVER – Sen. Barack Obama dropped in on his own party at the Democratic convention a day early Wednesday to praise his wife, his former rival, and former President Bill Clinton for going to bat for him.

“I think Michelle Obama kicked it off pretty well, don't you think?” Obama said, as delegates at the Pepsi Center roared.

Video Barack Obama made an unexpected appearance at the Democratic convention, joining his running mate, Sen. Joe Biden, on stage. Obama officially became the Democratic nominee on Wednesday. Media Player The FREE Windows Media Player is necessary to play Windows Media.

As his wife clapped and smiled and mouthed, “I love you,” Obama joined his running mate, Sen. Joe Biden, on the platform.

“If I'm not mistaken, Hillary Clinton rocked the house down last night!” Obama said.

He also praised former President Bill Clinton, who spoke earlier Wednesday night, as someone who reminds us about “what it's like when you've got a president who actually puts people first. Thank you President Clinton.”

Obama told the crowd he was proud to have “the whole Biden family on this journey with me to take America back.”

He said the convention was moving to Invesco Field at Mile High on Thursday because, “We want to open up this convention to make sure that everybody who wants to come can join in the effort to take America back.”

After his appearance, Obama made a late-night visit to Invesco Field to check out the stage where he will deliver his speech. He arrived with his wife, Michelle, and staff members.

Obama aides said he had substantially finished the speech he will deliver on Thursday night, but would probably continue to edit it right up until he delivers it Thursday night.

Senior strategist David Axelrod said Obama will lay out a case for sweeping political change and illustrate the choice voters face between his candidacy and that of Republican John McCain.

The stakes for the speech were high for Obama, a relative newcomer to the national stage who rose to prominence after delivering the keynote address at the Democratic convention in 2004. While that speech was widely praised as an inspirational stem-winder, Axelrod said Obama would use his nominating address to convey a more simple message about what he would do for the country as president.

“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.”

Axelrod said Obama had looked to past nominating speeches as models, including Bill Clinton's in 1992, Ronald Reagan's in 1980 and John F. Kennedy's in 1960.

Obama won't shy from drawing a stark contrast between himself and McCain, especially on economic matters. But he will do so in a respectful way, Axelrod said.