What do you call a U.S. senator who opposes the expansion of NATO to include the troubled former Yugoslav republic of Montenegro, a country that survived a (reportedly Russia-backed) coup attempt as recently as last fall? If you're Sen. John McCain (R-Ariz.), and that colleague is intervention-skeptic Rand Paul, you call him, remarkably, a pawn of Vladimir Putin.

"You are achieving the objectives of Vladimir Putin… of trying to dismember this small country," McCain lectured Paul on the Senate floor today. (Was it really just five weeks ago that Mitch McConnell silenced Elizabeth Warren over impugning the conduct and motives of a Senate colleague?) McCain then asked for unanimous consent for the Senate to approve Montenegro's accession into the U.S.-led military alliance, and Paul objected, before quickly exiting. That's when McCain got all voice-quivery and hand-choppy:

I note the senator from Kentucky leaving the floor without justification or any rationale for the action he has just taken. 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. And walk away! The only conclusion you can draw, when he walks away, 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. So I repeat again: The senator from Kentucky is now working for Vladimir Putin.

Watch it here:

In a follow-up statement, Paul said:

Currently, the United States has troops in dozens of countries and is actively fighting in Iraq, Syria, Libya, and Yemen (with the occasional drone strike in Pakistan). In addition, the United States is pledged to defend 28 countries in NATO. It is unwise to expand the monetary and military obligations of the United States given the burden of our $20 trillion debt.

McCain has been getting a lot of good press these days for the usual reason—occasionally opposing a Republican president that the press also doesn't like. Included in his latest round of re-mavericking are hosannahs for his brave stance against Trumpian conspiracy mongering. Will his friends in the press now point out that the Arizona senator has made a horrendous dual-loyalty charge against a sitting colleague with zero evidence aside from a procedural vote?

McCain has been slamming Paul over his supposed "isolationism" since 2010, famously calling him a "wacko bird" in March 2013, telling reporters a few months later that a Rand vs. Hillary presidential race would be a "tough choice," and unhappily sharing a Foreign Relations Committee seat with the Tea Party senator these past four-plus years. Paul has frequently returned the favor by using the phrase "stale and moss-covered." All of which is understandable, given their very different positions on an important issue central to both of them.

But just because Vladimir Putin dislikes an American policy doesn't make it automatically virtuous or wise. Part of the original conception of NATO expansion—which I, unlike 99 percent of libertarians, both favored and covered while it was happening—was that the new members had to be stable, with border disputes with neighbors fully resolved at the treaty level, substantial minority-population protections, and no pressing disputes with adversaries. Does that sound like Montenegro to you? Or Georgia, which McCain has been pushing for NATO inclusion since at least 2008 (and which Paul single-handedly blocked in 2011)?

Despite writing a book critical of his views, I have happily defended John McCain against scurrilous charges about his patriotism and heroism. To see him go rhetorically McCarthyite against a fellow American for having the temerity to disagree with his often questionable foreign policy judgment is one of the most disgraceful moments of his long career.