Yeah.. that's how tribalism works. Dems don't really understand the kind of blank-check popular backing that Trump has.
Studies have shown for a long time the human brain is frequently wired to prioritize group loyalty over factual accuracy. Probably something left over from when we were living in caves in small groups. Trump understands it extremely well. He just has to bring up immigrants and their brain reasoning centers turn off and they start frothing over Haitians eating dogs. Prior to Trump, most white Americans only encountered this if they brought a black girlfriend home.
After Obama, Trump literally rewrote the republican party. Congressmen who weren't falling in line got fired or forced to retire. Many many times, eg see Liz Cheney. The last time a purge like this happened was at the time of the Civil War. Even super-popular FDR tried taking out conservative democrats but wasn't successful (which btw is one of the main reasons we didn't get stuff like universal healthcare in the 1930s; southern democrats decided it was a threat to segregation).
That probably shows us how to stop it: wait for a massive failure like WW2 or the Great Depression, then implement strong safety nets, media, education, etc pretty much everything Western Europe is doing & more (eg housing).