Economics is a big one, but not the main explanation; the US has been in the doldrums but spared a major crisis, mostly because of Obama’s decisions. The loser mentality accounts for a much bigger explanation: the exact opposite of the can do mentality that did so much good for the US in the past.
The US elected a wrecker, but destroying is not enough, something has to be put in place of the current system, and he’s clueless; which means the necessary reforms will not take place in the next four years, and the economy will tank, hurting those who were reckless enough to vote for him the most.
A populist is someone who promises whatever you want to hear to get elected, but then has no idea how to deliver on what he promised.
In this Trump is no different than any other US politician; except he has the nerve to claim never to have made any such promises. A man is only as good as his word, and Trump has none.