With tens of thousands of Republicans gathering in Florida for the party’s national convention, former Gov. Charlie Crist tossed a political stink bomb into the festivities Sunday by endorsing President Obama for reelection.

Crist, an independent who abandoned the Republican Party during his 2010 run for U.S. Senate, bashed the GOP and praised Obama in an essay published by the Tampa Bay Times. Republican leaders reacted by calling Crist a “crass opportunist” angling to run for governor as a Democrat in 2014.