All countries have a rabid element in their electorate
In the UK it tends to run between 6% and 12%
In continental Europe it runs between 10% and 20%
In America it runs between 20% and 33%
America has a particularly deep seam of nasty opinion. Hillary Clinton wasn't far wrong when she described half of Trump's natural support as "deplorable" (although she should never have said it)
If I had to point to any single factor that's driven this, then its the wave of
never recovered (from the credit crunch). It's not as if history hasn't shown us this before. In the wake of a massive economic slump people don't automatically turn extreme, but if after about 7-8 years they haven't recovered their status then they become a lot more receptive to this type of messaging. They begin to resent data led recoveries, and being told by remote politicians that everything is back to where it was, when their own experiences are frankly contradicting this. It begins to manifest itself as a vote that I would describe as;
this ain't working for me any longer, may as well try it, what's the worse that can happen? Which I think accounts for a fair amount of Brexit antipathy
America has a couple of other issues that make them particularly vulnerable
In the first case they allow the poison of religion into the politics much more so than any other western country, and it tends to be a quite radical interpretation too. Ironically it was something Jimmy Carter first plugged into, but the Republicans have taken it to new levels
I think what's probably more relevant however is the breakdown in the relationship with the media post Iraq, which has coincided with the emergence of new social platforms. American news doesn't report. Instead it campaigns. It's perfectly possible now to take your news in an echo chamber of bias confirmation. Fox are appalling, but it also needs to be acknowledged that CNN and MSNBC are equally partisan, they just tend to produce more thoughtful content, even if the likes of Rachael Maddow would never be allowed to get away with the stuff she pumps out in the UK. Then of course you have this whole wodge of right wing websites like Brietbart, or Info Wars, plus their local radio is truly shocking
Perhaps the final piece in the jigsaw is their education system. Americans do actually make me laugh when they brag about their world class universities. Just ask how many of them went to one? The fault line is in the strata below. America is outside of the top-20 in all three of the PISA categories. In fact she was outside of the top-40 in maths. America spends 2% of her federal budget on education, and 7% on interest repayment (some education is picked up at state level of course). There seems to have been an insidious invasion however that has begun to celebrate ignorance in American culture
"War is Peace; Freedom is Slavery; Ignorance is Strength;"