 -- Sen. John McCain is prodding one of his closest allies in the Senate to consider a run for the White House – Sen. Lindsey Graham.

“I think he is looking at it, and I am strongly encouraging him to take a look at it,” McCain, R-Ariz., told ABC News. “I know of no one who is better versed and more important on national security policy and defense than Lindsey Graham, and I don’t think these challenges to our security are going away.”

“He is eminently qualified,” McCain added.

In an interview with The Weekly Standard last month, Graham, R-S.C., said he might consider a presidential bid after this year’s midterm elections if other candidates aren’t promoting an aggressive foreign policy agenda.

“If I get through my general election, if nobody steps up in the presidential mix, if nobody’s out there talking -— me and McCain have been talking -— I may just jump in to get to make these arguments,” Graham said.

On CNN's State of the Union Sunday, Graham said running for president is "the hardest thing one could ever do. You go through personal hell. You have got to raise a ton of money. I'm nowhere near there."

McCain, the 2008 Republican presidential nominee, said he expects a “very crowded field” in 2016 that will be compromised of both senators and governors.

“I think there's an old saying that if you are a United States senator that unless you are under indictment, or detoxification that you can automatically consider yourself a candidate,” McCain joked. “I think we should let a thousand flowers bloom. I think that the process is wide open right now, and I think not only will members of the Senate be considered, but I think some of our successful Republican governors will also be interested.”

While another presidential run isn’t in McCain’s future, the Arizona senator said he will “likely” run for a sixth term in the Senate when he’s up for re-election in 2016.

“Most likely I will, and I expect it to be a very tough race as I have every time, and I’m making every preparation,” McCain said. “As one of my Irish friends once said, a fight not joined is a fight not enjoyed.”