Lest you’ve forgotten the details, Sen. Joseph R. McCarthy Jr., a Wisconsin Republican, held much of the country in a demagogic grip a half-century ago. He intimidated most political leaders and most of the media with fanciful charges that Communists had infiltrated the State Department and successfully plotted to give Poland to Russia and turn China over to the Communists. He targeted Secretaries of State George Marshall and Dean Acheson to the alleged conspiracy. His downfall came when he tried to force the U.S. Army to give a favorable assignment to a young friend and when his televised hearings showed him up to be a bully and a fraud. “McCarthyism” became a term for false prosecution and guilt by association.

Now comes Ann Coulter and her new book, “Treason: Liberal treachery from the Cold War to the War on Terrorism” (Crown Forum). It’s a best seller, though partly because of mass purchases by her admirers. She portrays McCarthy as a martyr and suggests that we would all be slaves in Soviet-style prison camps were it not for his courage in exposing the Communist menace.

By the time the book came out, Ms. Coulter had already lost the sympathy of many conservatives. The editors of the right-wing National Review had dropped her column after she wrote of Muslim nations, “We should invade their countries, kill their leaders and convert them to Christianity.” Nonetheless, her rewriting of history and her diatribes against all liberals has made her a darling of the ultraconservative fringe that puts strident opinion above fact. She knows how to throw them red meat.

Much has been written about her book’s flaws and fallacies. But it remained for a writer for The Wall Street Journal’s conservative editorial page, Dorothy Rabinowitz, to do the best debunking job to date. She noted that the Coulter history of the Hollywood blacklist of suspected Communists ridicules the whining of prosperous exiles but ignores “the countless people destroyed because their names had popped up on some list of alleged Communists or fellow travelers, or sounded like a name on one of those lists.”

Ms. Rabinowitz also pointed out that Ms. Coulter’s admiring biography of Sen. McCarthy’s career “excludes the senator’s remarkable efforts on behalf of the members of the SS battle group who executed 86 American POWs in the Ardennes campaign in December 1944, otherwise known as the Malmedy Massacre.” His line was that the U.S. Army had cruelly mistreated the former SS men.

At the same time, she managed to express a rational conservatism. Noting that Ms. Coulter makes the point that members of the elite establishment all despised McCarthy, Ms. Rabinowitz goes on: “So did most educators, intellectuals and university faculties.” She adds that, dismal to note today, “the universities which were once hotbeds of opposition to McCarthy are now little worlds of their own, where political censorship, speech codes and other ideologically driven assaults on freedom are the accepted order of things.”

Readers can thank Ms. Rabinowitz for filling in the gaps in a gap-filled book.