https://www.nationalreview.com/corner/robert-mueller-trump-russia-investigation-history-witch-hunts/
Robert Mueller’s Russian-collusion investigation is often called a “witch hunt,” and there has been considerable debate over whether this is a proper description. For what it’s worth, the earliest known use of the phrase in American politics occurred a century ago this spring, and it involved Russian attempts to influence the U.S. government. In February and March of 1919, the Senate Judiciary Committee held hearings on “Bolshevik Propaganda,” and at one point the following exchange occurred between Raymond Robins, a progressive economist who advocated recognizing the Bolshevik regime, and Senator Lee S. Overman (D., N.C.) (emphasis added):
Mr. Robins. . . . And, Senator, I believe that when we know the beast, with the united intelligence of the free men and women of America, I have faith enough in our institutions to believe that we will throw that foreign culture, born out of a foreign despotism, back out of our land, not by treating it with the method of tyranny, not by a witch hunt, nor by hysteria, but by strong, intelligent action, the intelligent action of Senators of the United States making a report that gets before the people the truth of the situation and mobolizes [sic] the consciences and the intelligence of the men and women of our land.
Senator Overman. What do you mean by witch hunt?
Mr. Robins. I mean this, Senator. You are familiar with the old witch-hunt attitude, that when people get frightened at things and see bogies, then they get out witch proclamations, and mob action and all kinds of hysteria takes place.
Senator Overman. This committee has been called a witch hunt.
Mr. Robins. I wish to make no possible sort of criticism of the committee. I wish to say that I have never been treated more fairly than I have been here.
Nowadays the phrase is generally understood to refer to the witch trials of colonial New England, which, in the popular mind, are thought to have differed from modern-day criminal trials in several ways:
a) the outcome was often determined in advance;
b) shoddy, fabricated, or unreliable evidence was accepted;
c) they were motivated by a desire to scapegoat members of disfavored groups; and
d) the whole thing was ridiculous because the crime being prosecuted does not exist.