As the primary race intensified, Crist then flip-flopped on the stimulus, alternately bashing it and talking it up depending on the day or the media outlet he was addressing. Crist released a radio ad that bashed Obama for spending. The Florida Democratic Party later released a TV spot that questioned Crist’s authenticity.

Crist brushed aside those differences Thursday night.

“I’ll be honest with you, I don’t agree with President Obama about everything.,” Crist said. “But I’ve gotten to know him, I’ve worked with him, and the choice is crystal clear.”

Crist credited Obama with not only saving the economy in Florida, but for fighting to ensure that BP cleaned up the Gulf Coast after the oil spill. Crist said nothing Thursday about the president’s Affordable Care Act, which Crist once described as scary.

Crist’s role at the Democratic National Convention underscores the weakness of the party in Florida, where only Sen. Bill Nelson holds a statewide seat. The Legislature is overwhelmingly Republican, even though registered Democrats outnumber Republicans in the state.

Democrats want a winner. They note that, as an independent, he garnered 1.6 million votes in 2010 to Rubio’s 2.6 million. Democratic Rep. Kendrick Meek came in third, with just over 1 million votes, the overwhelming majority of which would likely have gone to Crist had there not been a three-way race.

Meek won’t rule out running for governor against Crist. Florida Senate Democratic leader Nan Rich, of Weston, is running. And former state Chief Financial Officer Alex Sink might want a rematch against Republican Gov. Rick Scott, who narrowly beat her in 2010.

“If by some miracle Charlie Crist makes it out of the gauntlet of a Democratic primary even though he called himself a staunch conservative, he then has to run on his dismal record,” said Scott’s political advisor and pollster Tony Fabrizio, who ticked off the dismal economic indicators that unfolded on Crist’s watch.

Former Miami Beach Democratic state Sen. Dan Gelber recently penned a column welcoming Crist to the party, and he chuckled at Republicans painting the former governor out as a flip flopper.

“Just a week ago,” Gelber said, “Republicans nominated Mitt Romney, a former pro-choice, pro-gay marriage, anti-Reagan economic, self-described progressive who used to be concerned about global warming.”

Crist steered clear of mentioning Romney’s reversals, but he did echo the Democratic talking point that the Republicans “would break the fundamental promise of Medicare and Social Security” — a line of attack that could prove devastating in must-win Florida, a state with a disproportionate share of elderly residents.

Crist’s speech was brief. Accustomed to having a fan at his side to keep cool, Crist didn’t have the luxury on Thursday night and was on the cusp of breaking into a sweat on stage.

But he ended quickly and smoothly as he started to win the home crowd, noting “I used to play quarterback just down the road from here at Wake Forest University. My dad always told me, ‘Charlie, it takes a cool head to win a hot game.’”

Crist said Obama had the “cool head” the nation needs.

"That's the leader Florida needs. That's the leader America needs," he said, as the crowd rose to its feet. "And that's the reason I'm here tonight."