"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."

He called Obama the "right leader for our times."

Crist could be one of several Republicans included at the Democratic convention, in an effort to prove Obama is willing to reach across the aisle. Crist, who was defeated by Marco RubioMarco Antonio RubioGOP Senate candidates trade barbs in brutal Indiana primary Students gather outside White House after walkout to protest gun violence Overnight Energy: Senate confirms Bridenstine as NASA chief | Watchdog probes Pruitt’s use of security detail | Emails shine light on EPA science policy changes MORE (R) in Florida's 2009 Senate race, has been criticized by conservatives for getting too friendly with Democrats. He switched his party affiliation to Independent in 2009.

The Democratic convention begins next Tuesday in Charlotte, N.C. The scheduled time of Crist's speech has not yet been released.