Ad hominem has always been a feature of politics, but Senator John McCain (R‑AZ) elevated it to a new level earlier this week. The incident occurred when McCain came to the Senate floor to ask for unanimous consent to move forward on a vote formally bringing Montenegro, a small country in the Balkans, into the NATO alliance. Senator Rand Paul (R‑KY) objected. McCain responded by suggesting Paul was a traitor to his country and accusing him of “working for Vladimir Putin.”

McCain seemed particularly incensed that Paul objected without explaining his reasons. As reported at the Daily Beast:

“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.”

He then directly connected Paul to the Russian government: “The only conclusion you can draw when he walks away is 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.”

Paul later issued a statement in response:

“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.”

That seems like a reasonable position to hold, and certainly not one that requires Paul to be a Russian stooge.

Indeed, many of America’s most reputable officials and academics have opposed post-Cold War NATO expansion for substantive reasons. George Kennan, perhaps our most famous Cold War diplomat and widely considered to be the father of the United States’ containment strategy, famously opposed NATO expansion in the 1990s, writing in the New York Times that expanding NATO would be a “fateful error” that would “inflame the nationalistic, anti-Western and militaristic tendencies in Russian opinion” and “restore the atmosphere of the cold war to East-West relations.” Like Senator Paul, Kennan also worried about the problems of credibility and overextension. Would McCain accuse Kennan of treason?

In 1995, a group of almost two dozen retired Foreign Service, State Department, and Department of Defense officers who served during the Cold War signed an open letter opposing NATO expansion on grounds similar to Paul and Kennan. They argued it risked exacerbating instability and “convincing most Russians that the United States and the West are attempting to isolate, encircle, and subordinate them.” The signatories included Paul H. Nitze, former Secretary of the Navy and Deputy Secretary of Defense, as well as Jack F. Matlock, Jr., former Ambassador to the USSR, and John A. Armitage, former Deputy Assistant Secretary of State for European Affairs. Were these gentlemen also secret Russian moles?

Within the academic international relations literature, there are a host of reasons to be skeptical of the wisdom of NATO expansion. Contrary to advocates of expansion, there is little reason to believe NATO expansion spreads democracy. Furthermore, scholars widely acknowledge that, in an attempt to expand Western security cooperation and deter Russian assertiveness in Eastern Europe, NATO expansion feeds Russian insecurities and provokes Moscow to take actions to preserve its sphere of influence in its near abroad. As Jonathan Masters of the Council on Foreign Relations explains, Putin cited NATO expansion to justify Russia’s military interventions in Georgia and Ukraine, a “clear signal of Moscow’s intentions to protect what it sees as its sphere of influence.”

Beyond the classic security dilemma, NATO expansion does not serve U.S. interests. Expanding security commitments to more European states puts U.S. credibility on the line with little to no strategic benefits in return. What happens in Montenegro does not affect our security as a nation, except that by taking on additional responsibilities to defend other countries, we risk being sucked into unnecessary conflicts that could otherwise be avoided. As MIT’s Barry Posen explains, “Once committed to defend allies everywhere, a state becomes obsessed with its political and military prestige, and vulnerable to the claim that ‘small’ wars must be fought in the hope of deterring large ones. This is especially true when the actual strategic value of these allies is modest.”

Notwithstanding Russia’s reprehensible actions in places like Georgia and Ukraine, Europe is a relatively benign security environment that doesn’t need to be under the American security umbrella. To the extent that Europe needs military capabilities to deter Russian aggression, the region is rich and powerful enough to provide for its own security.

It would be a shame if sensible, earnest, and well-informed perspectives continue to be shut out of the debate by slanderous accusations that opposition to NATO expansion is a signpost for treason.