MOSCOW — The phrase was too toxic even for Nikita Khrushchev, a war-hardened veteran communist not known for squeamishness. As leader of the Soviet Union, he demanded an end to the use of the term “enemy of the people” because “it eliminated the possibility of any kind of ideological fight.”

“The formula ‘enemy of the people,’” Mr. Khrushchev told the Soviet Communist Party in a 1956 speech denouncing Stalin’s cult of personality, “was specifically introduced for the purpose of physically annihilating such individuals” who disagreed with the supreme leader.

It is difficult to know if President Trump is aware of the historic resonance of the term, a label generally associated with despotic communist governments rather than democracies. But his decision to unleash the terminology has left some historians scratching their heads. Why would the elected leader of a democratic nation embrace a label that, after the death of Stalin, even the Soviet Union found to be too freighted with sinister connotations?

Nina Khrushcheva, the great-granddaughter of Mr. Khrushchev and a professor of international affairs at the New School in New York, said the phrase was “shocking to hear in a non-Soviet, moreover non-Stalinist setting.” Her great-grandfather, she said, “of course also used Soviet slogans and ideological idioms but still tried to stay away from sweeping denunciations of whole segments of the Soviet population.”