The American People's perceptions of the rival party are all Wrong!

begin partial quote from:https://time.com/6990721/us-politics-polarization-myth/

Why not ask “everyone else” whether America is really that divided? Pollsters do, all the time. But there’s a problem. Ordinary folks think Americans are much more partisan than they are. In the same study, people grossly overestimated (by 78%) the size of the most polarized group within each party—that is, Democrats who call themselves liberal and Republicans who call themselves conservative. At the same time, ordinary Americans grossly underestimated (by 77%) the share of the other party who are moderate. That share is, in fact, at least half of either party. “People probably are exactly right about how polarized their leaders are,” says Robb Willer, a sociologist at Stanford. “They get it very wrong for the general public.”

It gets worse: the more involved in politics a person is, the more distorted their view of the other side, a 2019 YouGov survey found. In other words, engagement in civic life actually serves to narrow one’s perspective on the world.

end quote.

So, what is it that causes people to be so wrong in their assumptions about the other party?

I think it's the hype of some places like Fox News and others both Nazi as well as Liberal that want people to appear to be polarized when they are not really as you can plainly see.