The biggest Florida speaker at the Democratic National Convention wasn’t a Democrat.

Yet.

After former Republican Gov. Charlie Crist’s speech Thursday night, it’s only a matter of time before he officially joins the party’s ranks in a slow march to running for governor in two years.

Crist’s high-profile role disturbed many Florida delegates, but it furthered President Obama’s campaign message — that the Republican Party is too extreme.

“As a former lifelong Republican, it pains me to tell you that today’s Republicans — and their standard-bearers, Mitt Romney and Paul Ryan — just aren’t up to the task,” Crist said. “They’re beholden to ‘my way or the highway’ bullies, indebted to billionaires who bankroll ads and allergic to the very idea of compromise.”

Crist’s speech was as much a condemnation of today’s Republican Party as it was an explanation of why he’s officially moving toward the Democratic Party and away from the conservative positions he once espoused.

Republicans and many Democrats alike won’t let Crist forget he campaigned for years as a pro-life, anti-gay marriage, gun-touting “Reagan Republican” and “Jeb Bush Republican.” In 2010, in his unsuccessful Senate bid, he bashed Obama’s agenda and ran as a “true conservative.”

“Is he here, and in this for his principles?” asked Democratic delegate Bob Hartnett of Orlando. “I’ve got a long time to think about that. But there are many others in this party qualified to lead and be onstage representing our people.”

Crist said Thursday that he was addressing the convention “not as a Republican, not as a Democrat, but as an optimist.” Crist referred to Bush in his speech as “my friend” — a comment sure to irk conservatives as well as Bush, who has described Crist as an opportunist.

Crist ran as a conservative in his first statewide race in 1998, when he unsuccessfully ran for U.S. Senate. With Bush’s help, Crist was elected education commissioner, attorney general and, in 2006, governor where he governed as a centrist.

“Half a century ago, Ronald Reagan, the man whose relentless optimism inspired me to enter politics, famously said that he didn’t leave the Democratic Party; the party left him,” Crist said. “I can certainly relate. I didn’t leave the Republican Party; it left me.”

But the timing of Crist’s departure from the Republican Party suggests a colder political calculation. He officially left the party just before a candidate-qualifying deadline in the 2010 Senate race.

Crist was running against fellow Republican Marco Rubio, and Crist would have handily lost the GOP primary. So he left the GOP and ran as an independent, though he ultimately lost the general election.

Crist’s undoing in the GOP: The infamous “hug,” his decision to appear onstage with Obama in 2009 in Fort Myers, where he literally embraced the president and the $787 billion stimulus program.

“That hug caused me more grief from my former party than you can ever imagine,” Crist said. “But even as the Republican Party fought tooth and nail to stop him, this president showed his courage, invested in America — and saved Florida.”

Crist was the only Republican governor to break ranks with his party to talk up the stimulus, which every GOP governor and Legislature wound up using to patch holes in their budget.