(CNN) - During his ill-fated presidential bid in 2008, Rudy Giuliani aggressively sought Charlie Crist's endorsement, hoping that the Florida governor's support would hand him a primary win in the state and shake up the GOP nominating contest.
Crist instead gave a last-minute endorsement to John McCain, who went on to win the pivotal primary. The former New York City mayor's chances of becoming president died then and there.
Giuliani's payback? He's endorsing Marco Rubio, Crist's opponent in this year's Republican Senate primary.
Giuliani will campaign with Rubio, the former state House speaker, in Miami on Monday morning.
"Marco Rubio is one of the Republican Party's true rising stars," Giuliani said in a statement released by the Rubio camp. "He's a bold leader who will bring common sense to Washington where it's badly needed. I look forward to campaigning with him on Monday."
McCain, the winner of that 2008 Florida primary, is supporting Crist.