DENVER, Colo. (NBC) - It's day one of the Democrats' convention in Denver. This afternoon, the doors of the Pepsi Center will open to thousands of delegates but not all of them are firmly behind Barack Obama.

Democrats have built this elaborate stage, hoping to electrify the party faithful and show unity these next four days. Tonight, you'll hear Michelle Obama telling her husband's story.

Michelle Obama has arrived in Denver. Later this morning, she'll tour the stage where tonight she tells America the story behind Barack Obama.

Sen. Obama says "and I think what you'll conclude is, gee he's sort of like us. He comes from a middle class background."

That's the Obama Democrats want voters to see, the poor kid who made it.

Now paired with the man Obama calls the "scrappy kid from Scranton."

Sen. Obama says "he's the right man for the job. He's got the passion to lift up middle class Americans. He hasn't forgotten his working class roots."

In a new video, Joe Biden, who'll be in Denver today, promises to speak out.

Sen. Biden says "I do it on behalf of the middle class and I plan to continue that approach in the months ahead."

But John McCain questions why Hillary Clinton isn't on the ticket.

Clinton's planning to give her delegates to Obama Wednesday but many are still bitter.

Clinton delegate Cheryl Benton says "we all ought to take a deep breath here and realize Barack Obama is our nominee, Joe Biden is our Vice Presidential nominee. We HAVE to come together."

Sen. Clinton says "The best way to continue this fight is to elect Barack Obama the next President of the United States!"

Analysts say for Obama to leave Denver with a unified party behind him, Clinton's speech Tuesday night needs to be more than just supportive it must be persuasive.

There are reports that Senator Ted Kennedy, who was diagnosed with a brain tumor not long ago, may speak against his doctor's advice. Tonight's program also includes a tribute to the Kennedy family.