In her 2003 book “Treason: Liberal Treachery From the Cold War to the War on Terrorism,” conservative pundit Ann Coulter launched a full-throated defense of Joseph R. McCarthy. Hardly the witch-hunting monster of liberals’ imagination, Coulter wrote, McCarthy was a patriot who protected his country from communists overseas and their apologists at home. Coulter’s assertion reflected an enduring belief in McCarthy among the Republican faithful, who continued to lionize him long after the Senate censured the senator and ended his career in disgrace.

More than a half-century later, however, the party has abruptly changed course thanks to one man: President Trump. Instead of praising McCarthyism, Republicans use the phrase “McCarthyism” to malign Democrats who dare demand answers about Trump’s ties to Russia. Trump himself fired the first salvo in the summer, tweeting that special counsel Robert S. Mueller III’s investigation into Russian election interference was “an illegal Joseph McCarthy style Witch Hunt.” And just last week, two GOP congressional leaders compared House Intelligence Committee Chairman Adam B. Schiff (D-Calif.) — one of the investigation’s key supporters — to, yes, McCarthy.

Liberals came quickly to Schiff’s defense, noting that nothing in the Russia probe came close to the deceit and destruction of McCarthyism. But in a perverse way, these charges reflect a crucial concession by Republicans after seven decades of denial: McCarthyism was, in fact, a massive, unpardonable assault on freedom, fairness and the rule of law. And strange as it may seem, we owe that new consensus to Trump.