Sen. John McCainJohn Sidney McCainMeghan McCain on Pelosi-Trump feud: 'Put this crap aside' and 'work together for America' Meghan McCain says Ben Carson should be developing brain cancer treatment, not working at HUD Graham urges Trump not to abandon infrastructure talks with Democrats MORE on Tuesday acknowledged he is trying to persuade Rep. Mike Castle (R-Del.) into running for the Senate, saying he has had informal conversations about the possibility of Castle running for Vice President Joseph Biden's former seat.

"He's had an outstanding record of service, and I told him someone with his background and experience would have an immediate impact in the Senate," McCain said of Castle. "He has a very good record that I
think is distinctive for Delaware."

McCain also said he advised Florida Gov. Charlie Crist into making the choice he announced Tuesday, that he will run for Sen. Mel Martinez's seat.

McCain and Crist have a noteworthy history--Crist's endorsement helped put McCain over the top in last year's GOP presidential primary in Florida, and Crist made the short list of vice presidential prospects for McCain later in the year.

"I support him, and he was very important to me in the primary," McCain said. "We've talked several times. I told him, 'Run.' We need him... I know him very well, and he's very qualified. I have great respect for the other candidates, but he's mine."

--J. Taylor Rushing