exploit the very real and relevant economic concerns of economically disadvantaged, minimally-educated (I say this in a demographic sense, not in a intellectual snobbery sense) people in areas with little ethnic diversity.
Not sure if it's still the case here, but at one point I saw an analysis that said, in France, the Front actually does best in areas with no immigrants. I suppose it plays to the fears about "it could happen here" - whereas those who live in more integrated areas realize that folks is folks.
Unfortunately, the US has a long history of tricksters, hucksters and con artists - in politics and all other walks of life. I keep thinking of the musical The Music Man, with the song "We've got trouble, right here in River City."
They have also not suffered a real war on their own turf since the mid 1800s, so can get all "excited" by talk of fighting, carpet bombing and "taking out" the Bad Guys, as long as they are oceans away. There is this tough guy image to be maintained - and Trump plays that part particularly well, though if he were (God forbid!) to wind up as President, I think it won't take long for him to unravel. (Though they claim to respect each other, I suspect Putin would eat him for lunch pretty early on.)
And yet another "nightmare scenario" has the (other) billionaire, Mike Bloomberg, jumping in to "save the day" as a third party candidate. The problem with that is that, under the strange Electoral College voting scheme they have in the US, this could actually work in Trump's favor.
(Short explanation: the President is not elected by popular vote of the people, but rather by the delegates elected in each State, sort of like the primary process. There have been several times that the President elected is NOT the one who received the majority of the popular vote.)