Some of these arguments are made in earnest; others perhaps are mere efforts to be edgy. One might think they’re harmless, but they potentially influence millions of American conservatives, and Russian state media has republished some of them to push the lie that Ukraine is overrun by Nazis targeting Russian civilians. They also damage the credibility of the America-first movement.

Some of my former colleagues buy into Mr. Putin’s false narratives because they mistake him for a Russian Donald Trump—a strong nationalist leader who fights woke ideas. But the war against Ukraine hasn’t benefited Russians, and Mr. Putin is a ruthless dictator with contempt for human life, including the lives of Russians. The Russian opposition he represses is “liberal” not in the sense of being leftist but of favoring freedom. His opposition to the North Atlantic Treaty Organization isn’t antiglobalist but anti-Western and anti-American.

Still, that so many leading America-firsters are parroting the Kremlin’s narrative suggests the movement has taken a dangerous turn. The reasonable goal of reducing military adventurism has regressed toward extreme isolationism, producing a self-described antiwar movement that preaches peace while callously ignoring war crimes.