Walter Russel Mead. who always seems to have something useful to say, has a good article in the current American Interest: The Meaning of Mr Trump.
Mead argues that the nation has moved on, but the professional establishment politicians haven't. They are still selling the same ideas and messages that they were selling a decade or two ago, but by now it is clear that these policies aren't working. He doesn't necessarily think that Trump has the answers, just that people are supporting Trump (and Bernie) as a message to the establishment that things aren't working.
I tend to agree. Although by comparison America is doing better than most of the rest of the world, it is nevertheless in trouble. The middle class is getting hollowed out, inequality is rising, the political systems is deadlocked and ineffective, government agencies right and left are getting mired in scandal (the VA system, the IRS, the Justice Department, etc, etc.), the economy is recovering at a snail's pace, we are mired in endless, wildly expensive wars in the Middle East, we seem to be helpless against the provocations of Russia and China, etc, etc, etc.
It's a good article.