I am too young (just barely) to remember the McCarthy Era in U.S. politics. If you’re blessed to be that young, McCarthyism, named after Senator Joseph McCarthy of Wisconsin, was, as explained in the Encyclopedia Britannica, a “period of time in American history that saw Wisconsin Sen. Joseph McCarthy produce a series of investigations and hearings during the 1950s in an effort to expose supposed communist infiltration of various areas of the U.S. government. The term has since become a byname for defamation of character or reputation by means of widely publicized indiscriminate allegations, especially on the basis of unsubstantiated charges.” (https://www.britannica.com/topic/McCarthyism )
McCarthyism has since been discredited, and today it’s not considered one of the more enlightened periods of U.S. history. So how do these things happen?
Big surprise — science has a explanation. It’s called the “illusory truth effect,” and it means something is considered true after it’s repeated enough times. It was first named in a 1977 research paper which found the positive feeling we experience when we hear true information is similar to the feeling we get when we hear information multiple times. In other words, repetition becomes evidence of truth (https://thedecisionlab.com/bias/illusory-truth-effect/). The effect must now be considered true itself; googling the term gets about 21,400 hits. As you might imagine, this has applicability to politics, advertising, and even medical research, as with Alzheimer’s disease.
Reading about this triggered something related I’ve found mentioned in history many times — the “Big Lie,” the bigger the lie, the more likely it is to be believed (https://www.urbandictionary.com/define.php?term=The%20Big%20Lie). Some attribute this to Adolf Hitler; others claim Hitler actually accused his enemies of using it. That term gets a lot more hits, although it can have meanings outside of politics; it’s a popular song lyric. No matter who thought of it first, politically it can be a potent propaganda technique.
So now we have social media. Our more current problem is just how do you tell fact from fiction? It’s becoming harder and harder, especially when foreign powers get involved. I would recommend consulting many sources, and keeping a very skeptical mind. I guess we need something less illusory and more truthful.