I will try to answer the question as someone who didn't vote for him but can understand why others did.
Feckless GOP, corruption in politics, Black lives matter, violence and riots in the cities, Obamacare, worse recovery in decades, mounting debt, declining middle class, deteriorating race relations, open borders, Hillary Clinton, college snowflakes demanding protection from free speech, Yale and Harvard professors who think they know what's best for everyone else, a media that views Middle America as the enemy, Middle East in a mess.....