WATCH: Cold War historian explains why Trump -- not Robert Mueller -- is the true heir to Joe McCarthy
Historian Tim Naftali appears on CNN (Screen cap).

Tim Naftali, a historian who teaches at New York University and who has written extensively about the United States during the Cold War, told CNN on Monday that President Donald Trump is the late Sen. Joe McCarthy's true heir.

Naftali made the comparison between Trump and McCarthy while reacting to a tweet the president sent out this weekend in which the president compared special counsel Robert Mueller to the late Wisconsin senator.

"What he said about Mueller is beyond outrageous -- it's poisonous," the historian explained. "Let's step back for a minute and talk about Joseph McCarthy. The United States faced a problem, in that the Soviets were penetrating the U.S. government... there was a reason to be concerned. Joseph McCarthy sees a political opportunity -- he's not talking to people in the FBI who know the real story, he's not talking to people in the CIA. He starts making up figures and saying, 'There are 200 Soviet agents in the State Department.'"

Naftali then drew a line between McCarthy's behavior and Trump's own habit of making fact-free claims about his opponents.

"Who in our political universe today is taking natural fears that Americans might have about ISIS, about terrorists, and fanning them for political gain?" he asked. "I don't think it's Robert Mueller."

Watch the video below.