John McCain puts on another display to remind us why he should never be taken seriously on foreign policy:

Sen. John McCain accused fellow Republican Sen. Rand Paul of “working for Vladimir Putin” on Wednesday.

The fireworks came as McCain spoke in support of a Senate unanimous consent request in support of Montenegro’s bid to join NATO. The libertarian-leaning Paul, who has often advocated for a less interventionist foreign policy, opposes the resolution.

McCain’s accusation is obnoxious, but it also shows how weak the case for bringing Montenegro into NATO is. If there were a strong argument in favor of adding a new member, McCain wouldn’t have to stoop to attacking Paul as a Russian pawn, but there isn’t and even he knows that. There are many good reasons why NATO shouldn’t let Montenegro join, not least of which is that it won’t make America or NATO more secure, but it is much easier for McCain to impugn the motives of his opponents than it is to answer their objections. Sen. Paul deserves credit for opposing the unthinking endorsement of continued NATO expansion. If bringing Montenegro into the alliance is worth doing, it should be properly debated and members should vote on the record. McCain wants to avoid that debate, because there is very little for his side of the debate to say other than to engage in fear-mongering and baseless accusations.

McCain has shown time and again that his judgment on foreign policy is not to be trusted, and he has confirmed that once again with his latest outburst.

Update: Paul later issued a statement to explain his opposition to taking on a new ally:

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.

Second Update: Matt Welch doesn’t think much of McCain’s outburst:

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.