Former Republican Florida Gov. Charlie Crist on Sunday endorsed President Obama, calling him the "right leader for our times."
"I applaud and share his vision of a future built by a strong and confident middle class in an economy that gives us the opportunity to reap prosperity through hard work and personal responsibility," said Crist, in an op-ed published in the Tampa Bay Times.
"Many have already forgotten how deep and daunting our shared crisis was in the winter of 2009, as President Obama was inaugurated," he added. "It was no ordinary challenge, and the president served as the nation's calm through a historically turbulent storm."
Rubio, popular with the Tea Party, is seen as a rising star within the GOP and was rumored to be on Mitt Romney's vice presidential short list. Rubio will introduce Romney on the last night of the Republican National Convention in Tampa, Fla. this week.
Crist, though, has thrown his support behind Democrats before. Earlier this month he attended a fundraiser for Democratic Sen. Bill Nelson's reelection bid.
Florida Republican Party Chairman Lenny Curry called Crist's endorsement a "repugnant."
"Today we have seen a repugnant display from a self-centered, career politician. While the people of Florida, and thousands of visitors who've traveled here, are facing an emergency, Charlie Crist has demonstrated, yet again, that his political ambition will always come first," said Curry in a statement, according to reports.
"For Crist to pull this Obama stunt while Florida faces a hurricane only proves Charlie Crist cares about just one thing: Charlie Crist," he added.
State officials are preparing for Tropical Storm Isaac, which forecasters say could gain hurricane force strength on Sunday and is headed from the Caribbean to Florida and the Gulf of Mexico. The storm has already forced the Republican National Committee to delay the convention in Tampa until Tuesday.
In his op-ed, Crist blasted his former party, accusing Republicans of adopting positions outside of the mainstream.
"As Republicans gather in Tampa to nominate Mitt Romney, Americans can expect to hear tales of how President Obama has failed to work with their party or turn the economy around," he wrote. "The truth is that the party has failed to demonstrate the kind of leadership or seriousness voters deserve."
Crist on Sunday also defended his support for Obama's stimulus measures, a decision some say cost him his Senate bid. Crist said he "didn't stand with our president because of what it could mean politically."
“I did it because uniting to recover from the worst financial crisis of our lifetimes was more important than party affiliation. I stood with our nation's leader because it was right for my state," said Crist.
During his Senate primary bid, Rubio hit Crist over his support for President Obama's $787 billion stimulus package, a decision which angered many Florida Republicans. Rubio's campaign pushed a photograph of Crist welcoming Obama at a rally for the stimulus package in early 2009, costing Crist support among the party's conservative base.