The following is from Richard Hofstadter's "Anti-intellectualism in American Life":
"The McCarthyist fellow travelers who announced that they approved of the senator's goals even though they disapproved of his methods missed the point: to McCarthy's true believers what was really appealing about him were his methods, since his goals were always utterly nebulous. To them, his proliferating multiple accusations were a positive good, because they widened the net of suspicion and enabled it to catch many victims who were no longer, or had never been, Communists; his bullying was welcomed because it satisfied a craving for revenge and a desire to discredit the type of leadership the New Deal had made prominent. . . "These days anti-communism no longer carries the weight it once did, so let's substitute anti-immigrant, anti-Muslim, and anti-Mexican. Anti-intellectual cum anti-elitist serves as well in both contexts. And let's expand New Deal to include its continuations into Medicare, Medicaid and, obviously, Obamacare. With those changes made, Hofstadter, who published his classic in 1962, describes Donald Trump no less than Joseph McCarthy.
Sam Tanenhaus, in the current Atlantic**, takes the McCarthy comparison further, connecting Trump's ability to get mileage out of mass media, even while attacking it, to McCarthy's:
McCarthy had a second constituency--the media. To Eisenhower it seemed that the press, at once credulous and cynical, was building up McCarthy. In a speech to newspaper publishers, he accused journalists of cheap sensationalism, of presenting "clichès and slogans" instead of facts. Walter Lippmann, the most respected columnist of the time, was indignant: How could a responsible press not report what McCarthy said? The same quandary attends the media today, as they figure out how to handle "fake news" and the president's intemperate tweets. Now, as then, no good solution exists. . .
Though it might be overkill to bring it up, there is also the flesh and blood connection: Roy Cohn, McCarthy's hatchet man, was Trump's tutor.