DENVER, Colo. (NBC NEWS)- Tuesday night, America will hear what could be one of the most influential speeches of the presidential campaign: Hillary Clinton's pitch for Barack Obama.

As we wait to hear what Clinton will say, let's take a look back at Michelle Obama. She was the keynote speaker Monday night at the Democratic National Convention in Denver, but had a tough act to follow. Sen. Ted Kennedy wasn't supposed to be there, but spoke anyway. When he walked onto the stage, the crowd went wild.

For Democrats, it was as close to magic you could get.

Kennedy said "nothing, nothing is going to keep me away from this special gathering tonight."

The party's patriarch, weakened by chemotherapy, was determined to be the energizer, the unifier his party needed.

Kennedy said "we can meet these challenges with Barack Obama. Yes we can, and finally, yes we will."

Michelle Obama explained how her humble upbringing and her husband's work with the poor define who they are and who they hope to become.

"Barack and I were raised with so many of the same values: that you work hard for what you want in life; that your word is your bond and you do what you say you're going to do," Michelle Obama said.

Barack Obama joined them live via satellite from Missouri.

His big speech comes Thursday.

Sen. Obama said "I'm not aiming for a lot of high rhetoric. I'm much more concerned with communicating how I intend to help middle class families live their lives."

His running mate, Sen. Joe Biden got a warm welcome. He speaks Wednesday.

But first, Sen. Hillary Clinton will try to heal the rift.

"We are united behind Barack Obama and Joe Biden," Clinton said.

Tuesday night, Clinton must do more than just state her support. She's got to make the hundreds of delegates in her corner believe it.

Now, Republicans aren't just sitting back watching all this. They have a "response center" in Denver, and are firing off several press releases a day slamming Obama and Biden. Tuesday, they're hosting a happy hour for Clinton supporters.

You can watch the Democratic National Convention on NBC Augusta from 10 to 11 p.m. this evening. The Republican National Convention begins Monday.