Nearly 70 years after Joseph McCarthy produced his first list of alleged government subversives at a West Virginia Republican banquet, the Wisconsin senator still haunts us. As historians and others ransack the American past searching for predecessors of our current president, McCarthy’s name often tops the list—but usually for the wrong reasons.

Even though the Donald doesn’t drink and “Tail-Gunner Joe” was a lush who died of liver failure, the two men are similar in many trivial and not-so-trivial ways. Like McCarthy, Trump is a sociopathic personality whose aberrant behavior facilitated a right-wing campaign against core democratic values.

Consistency is neither man’s hobgoblin. As blatant opportunists, neither was or is loyal to anything beyond themselves. After initially flirting with the social liberalism of their day, both switched parties and ideologies. During his early career as a judge in Appleton, Wisconsin, McCarthy was criticized for granting the quickest divorces around (at a moment when divorce was still considered scandalous, something reserved for abandoned women and film stars). While in his pre-Republican mode, Trump was a self-professed New York Democrat who was once, as he told Meet the Press in 1999, “very pro-choice.”

The two men have a remarkably similar relationship with the truth. McCarthy, like many politicians, exaggerated his wartime record while publicizing his ever-changing lists of—was it 81, 57, 205?—Communists in the State Department. No need here to detail Trump’s prevarications. The Washington Post says it’s an average of six or seven a day. Denial is his default mode.

In this, Trump may well have been following the advice of McCarthy’s former staffer, the notorious legal sleaze Roy Cohn, whose good connections and tainted ethics enabled him to service both McCarthy’s irresponsible allegations as well as the current president’s unprincipled business dealings. ...