Former Florida Gov. Charlie Crist, the Republican-turned-independent who just announced his endorsement for President Obama, plans to speak at the Democratic National Convention next week in Charlotte, N.C., a Democratic official confirms. 

While a get for Democrats, the speaking assignment appears to complete what has been a steady drift away from the Republican Party. Crist shed his GOP membership to run as an independent for Senate in 2010, but lost to Republican Marco Rubio -- who is speaking at the GOP convention in Tampa this week. 

Crist snubbed his former party again when he published an op-ed in Sunday's Tampa Bay Times endorsing Obama. He lamented an "element" of the GOP that plays to the "extreme right" and hailed Obama's economic stewardship in trying times -- just about the opposite message that Republican leaders will be sounding on the Tampa convention stage this week. 

"The president served as the nation's calm through a historically turbulent storm," Crist wrote. 

Republicans panned the op-ed as a political move by Crist, amid speculation that he's gearing up to run against GOP Gov. Rick Scott in 2014. 

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"He wants us to accuse him of being a liberal. Calling him a liberal will only play into his hand," a Republican PR firm claimed Sunday. 

Democrats are apparently looking to sustain the themes from that op-ed with his convention speech next week. The Democratic official told Fox News that Crist will address the "progress we've made in rebuilding our economy from the middle out, not the top down." 

"Gov. Crist can personally speak to this, and contrast the president's vision with Mitt Romney's, which caters to the most extreme elements of the Republican Party and undermines the middle class," the official said. 

Crist isn't the only party cross-over making a splash at the conventions. Former Democratic Alabama Rep. Artur Davis, who has changed his affiliation to Republican, is already in Tampa preparing for his speech to the GOP convention Tuesday. 

Fox News' Mike Emanuel contributed to this report.