Good article if you have time.

How Millions Were Duped By Russiagate: The "Illusory Truth" Effect

"........The answer is that they were told that the Russiagate narrative was legitimate over and over again by politicians and mass media pundits, and,  because of a peculiar phenomenon in the nature of human cognition,  this repetition made it seem true.

The rather uncreatively-named illusory truth effect describes the way  people are more likely to believe something is true after hearing it said many times.  This is due to the fact that the familiar feeling we experience when hearing something we’ve heard before feels very similar to our experience of knowing that something is true. When we hear a familiar idea, its familiarity provides us with something called cognitive ease, which is the relaxed, unlabored state we experience when our minds aren’t working hard at something. We also experience cognitive ease when we are presented with a statement that we know to be true.

We have a tendency to select for cognitive ease, which is why confirmation bias is a thing; believing ideas which don’t cause cognitive strain or dissonance gives us more cognitive ease than doing otherwise.  Our evolutionary ancestors adapted to seek out cognitive ease so that they could put their attention into making quick decisions essential for survival, rather than painstakingly mulling over whether everything we believe is as true as we think it is. This was great for not getting eaten by saber-toothed tigers in prehistoric times, but it’s not very helpful when navigating the twists and turns of a cognitively complex modern world. It’s also not helpful when you’re trying to cultivate truthful beliefs while surrounded by screens that are repeating the same bogus talking points over and over again. ...."

"....This explains why we all know people who are extraordinarily intelligent, but still bought into the Russiagate narrative just as much as our less mentally apt friends and acquaintances.  Their intelligence didn’t save them from this debunked conspiracy theory, it just made them more clever in finding ways of defending it. This is because the illusory truth effect largely bypasses the intellect, and even one’s own stored knowledge, because of the way we all reflexively select for cognitive ease. ...."

https://www.zerohedge.com/news/2019-03-26/how-millions-were-duped-russiagate-illusory-truth-effect