Sen. John McCain, R-Ariz., and fellow Republican Sen. Rand Paul of Kentucky have exchanged sharp public blows this week.

The most recent shot came from Paul on Thursday.

“I think he makes a really, really strong case for term limits. I think maybe he’s past his prime. I think maybe he’s gotten a little bit unhinged,” Paul said on MSNBC’s “Morning Joe” in reference to the 80-year-old Arizona senator.

Paul was addressing McCain’s comments about him on the Senate floor the day before. McCain was speaking in support of a bill that would help Montenegro, a small country bordering Serbia, take steps to join NATO. Noting Paul’s opposition to the measure, McCain mentioned the alleged attempted coup in Montenegro in late 2016, which the government said was orchestrated by Russian President Vladimir Putin.

“If there is objection, and I will note the senator from Kentucky is on the floor, and I will say before I read this, if there is objection, you are achieving the objectives of Vladimir Putin,” McCain began.

“You are achieving the objectives of trying to dismember this small country that has already been the subject of an attempted coup. I have no idea why anyone would object to this, except that I will say, if they object, they are now carrying out the desires and ambitions of Vladimir Putin, and I do not say that lightly.”

In response, Paul repeated his objection to the bill and then immediately left the chamber. McCain then launched into a direct attack on the Kentucky senator.

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

“The only conclusion that can be drawn when he walks away is that he has no argument to be made. He has no justification for his objection to having a small nation that is under assault from the Russians be part of NATO. So I repeat again: The senator from Kentucky is now working for Vladimir Putin.”

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Though both men, former presidential candidates, belong to the same political party, they often differ on foreign policy, with Paul advocating for a noninterventionist approach much of the time, often citing the financial burden of the more hawkish foreign policy that McCain favors.

“I do think that when we talk about NATO there can be a rational discussion about the pros and cons of expanding it,” Paul argued on “Morning Joe.”

“One of my favorite articles of that last couple years was one that talked about ‘the angry McCains’ and if we put active troops and got involved in combat where McCain wants us to be … it’s virtually everywhere,” he continued. “So his foreign policy is something that would greatly endanger the United States, greatly overextend us, and there has to be the thought whether or not it’s in our national interest to pledge to get involved with war if Montenegro has an altercation with anyone.”

In a February interview on ABC’s “This Week,” Paul made a similar point about his Senate colleague.

“John McCain is the guy that has advocated for war everywhere,” he said. “He would bankrupt the nation. Actually we’re very lucky John McCain is not in charge because I think we would be in perpetual war.”