In an interview with the New Republic, Sen. John McCain (R-Ariz.) acknowledges, laughingly, that a 2016 presidential race between former Secretary of State Hillary Rodham Clinton and Sen. Rand Paul (R-Ky.) would be "a tough choice" for him.

"When Hillary Clinton v. Rand Paul occurs in 2016, I guess you are going to have to decide who to vote for, huh?" TNR asked.

McCain responded with a chuckle: "It's gonna be a tough choice."

He then added: "Let me just clarify that. I think that Rand Paul represents a segment of the GOP, just like his father. And I think he is trying to expand that, intelligently, to make it larger."

McCain has quarreled repeatedly with Paul over national security and foreign policy issues, with McCain's hawkish style clashing with Paul's more libertarian, limited-intervention style. At one point, McCain labeled Paul and his ilk "wacko birds."

McCain has also had -- at times -- a nice relationship with Hillary and Bill Clinton, and the two said nice things about each other during the 2008 campaign. More recently, however, McCain emerged as a chief critic of the Obama administration and of Hillary Clinton's State Department for its handling of the attacks on a U.S. mission in Benghazi, Libya, in which four Americans were killed.

In the TNR interview, McCain called Clinton a "rock star" and said she did a "fine job" as secretary of state.

"She has, maybe not glamour, but certainly the aura of someone widely regarded throughout the world," McCain said. "I do think it is interesting that the issues where John Kerry is engaging is where Hillary Clinton did not engage in, that those decisions were left to the White House and the National Security Council."