The desire for a strong man
As others have said: democracy is messy, but this is the best that we can do.
In many countries and for many decades voters longed for a strong man who would fix everything, mostly bureaucracy, but often corruption. Thus, we've seen it in Russia that after the fall of the "organized" Communist regimes, many longed for it.
We've seen it with Hitler and Mussolini, of course, and we see it now in the Philippines, in Brazil and in other countries.
When i was in high school (many years ago) a poll found that many high school students wished for a dictator to "take care of things." My history teacher, a Holocaust survivor was shocked: do any of you know what it means to have someone knocks on you door in the middle of the night? To have the head of the household being removed never to be heard again? he asked.
Here, in this country, we long for a "businessman" who knows how to run business efficiently. This is why Ross Perot, in 1992, gathered so many supporters. And it does not matter for many that successful businessman are successful for, among other things, get rid of losing assets which, in a country, would mean non productive people: the poor, the sick and the elderly. And, I suppose, many would conclude that "it is not me."
Thus, in 2016 many had a similar wish for a "successful businessman," who would "clean the swamp." Never mind that many of his appointees were swamp kings.
I think that it will not take historians, looking back with an appropriate perspective, to conclude that Trump has been the most successful conman in our history. Not "self made" - he got his "business" from daddy, and then promptly drove it to the ground with all his bankruptcies.
It would be nice to incorporate this into the 2020 campaigns, but will his supporters even bother to listen?