OF ALL the strangely accommodating remarks President Trump has made about Russian President Vladimir Putin, none is quite so startling and pernicious as his suggestion that the United States is morally equivalent to a ruthless regime whose critics keep getting murdered. For all its flaws, the United States is fundamentally different from the Russia of Mr. Putin, whose relentless pursuit of hegemony over his neighbors and the degradation of the West is founded in cynicism. Every U.S. president prior to Mr. Trump has embraced a contrary vision of American exceptionalism in which the country serves as a beacon of democracy, human rights and the rule of law. For Mr. Trump to casually equate the two is as false as it is shocking.

Mr. Trump was interviewed by the Fox News commentator Bill O’Reilly for a broadcast just before the Super Bowl. Mr. O’Reilly brought up Russia, and pithily declared: “But he’s a killer, though. Putin’s a killer.” Mr. O’Reilly may have been referring to the many critics of Mr. Putin and his regime who have died in the past 17 years, including the opposition leader Boris Nemtsov, shot in the back near the walls of the Kremlin in 2015; anti-corruption investigator Sergei Magnitsky, who died in prison in 2009; former KGB man Alexander Litvinenko, poisoned with polonium in 2006; respected journalist Anna Politkovskaya, shot the same year; and journalist Yuri Shchekochikhin, thought to have been poisoned in 2003. In these cases and others, arrests have sometimes been made of the person who carried out the killing but not of those who ordered it.

Mr. Trump replied, “There are a lot of killers. We’ve got a lot of killers. Well, you think our country’s so innocent. You think our country’s so innocent?” Mr. O’Reilly: “I don’t know of any government leaders that are killers.” Mr. Trump: “Well — take a look at what we’ve done too. We made a lot of mistakes. I’ve been against the war in Iraq from the beginning.” Mr. O’Reilly: “But mistakes are different than — ” Mr. Trump: “A lot of mistakes, but a lot of people were killed. A lot of killers around, believe me.”

To state the obvious, in the United States, critics of the president are not poisoned or gunned down. By suggesting that U.S. military operations in Iraq — a country the George W. Bush administration invaded to depose a blood-soaked dictator — are equivalent to such crimes, Mr. Trump repudiates the very notion of a foreign policy based on values. He equates the forces of liberty and thuggery — and thereby validates strongmen everywhere who rule by coercion, suffocate free speech and crush individual dignity.

The United States is, of course, far from perfect: Its history includes dark chapters both at home and abroad. But as President Barack Obama observed, American exceptionalism lies in its elevated aspirations, and in the nation’s capacity to reverse its errors through democratic reform. Rather than embrace that tradition, Mr. Trump’s rhetoric suggests he will mimic Mr. Putin in the naked pursuit of narrow interests and disregard for legality and morality. It is a doctrine that leaders of both parties, along with ordinary Americans, should repudiate.