Eliza Collins

USA TODAY

Rand Paul thinks it might be time for John McCain to retire from the Senate because “maybe he's gotten a little bit unhinged."

"I think he makes a really, really strong case for term limits,” the Kentucky Republican said Thursday morning on MSNBC. “I think maybe he's past his prime.”

McCain, a Republican from Arizona, is 80 years old and was just elected to his sixth term in the Senate in November.

Paul’s comments followed McCain’s accusation Wednesday that Paul was working for the president of Russia.

"The senator from Kentucky is now working for Vladimir Putin," McCain said on the Senate floor after Paul blocked a bipartisan attempt to vote on a treaty that would allow Montenegro to join NATO.

McCain, who chairs the Senate Armed Services Committee, had joined Democratic colleagues to push for debate on the treaty. Paul objected the motion and then left.

"I note the senator from Kentucky leaving the floor without justification or any rationale for the action that he has just taken," McCain said. "That is really remarkable, that a senator blocking a treaty that is supported by the overwhelming number — perhaps 98 at least of his colleagues — would come to the floor and object and walk away."

"The only conclusion that you can draw is he has no argument to be made he has no justification for his objection to having a small nation be part of NATO that is under assault from the Russians,” McCain continued.

Paul does not support expansion of the military alliance and has previously blocked a treaty to allow Montenegro in.