Republican

Credit: Reuters/Steve Nesius

Former Florida Republican Governor Charlie Crist, who campaigned for U.S. President Barack Obama in the 2012 presidential election, speaks to the media in St. Petersburg, Florida, December 13, 2012.

Crist, who served as Florida's governor from 2007 to 2011, could not be immediately reached for comment. He has scheduled an event on Monday to announce his plans.

Florida Republican Governor Rick Scott will seek reelection in 2014 in what is expected to be one of the most expensive governor's races in the country.

With Republicans controlling every state house across the South, a Democratic gubernatorial win in Florida - the first in two decades - could significantly alter the political landscape in the run-up to the 2016 presidential race.

Crist, who abandoned the Republican Party after losing a U.S. Senate primary to Marco Rubio in 2010, has repeatedly criticized Scott, who opinion polls show ranks among the nation's most unpopular governors.

A Quinnipiac poll in June measuring a potential Scott-Crist match-up gave the newly minted Democrat a commanding lead over Scott, a wealthy former healthcare executive.

In recent weeks, Florida Republicans have kept up a daily drumbeat of Internet and media attacks on Crist, calling him untrustworthy and citing his change from a conservative Republican to a moderate Democrat.

On Friday, Florida Republican Party Chairman Lenny Curry criticized Crist, who after his first time as governor decided to make his Senate bid.

'Charlie Crist has now officially filed to run for the position he once abandoned,' Curry said in a statement. 'When Florida needed Charlie Crist the most during difficult economic times, he ran away. If he really wants to be governor now, why did he quit the first time?'

(Additional reporting by Bill Cotterell in Tallahassee; Writing by Kevin Gray; Editing by Tim Dobbyn)