Exactly what has he done that is so bad?
Glad you asked. Here is a very much abbreviated list.
1) Condoned* the separation of parents and children in Federal detention and the losing track of them. Then acting with indifference when courts demanded that the children be return to their parents.
2) Founded a Fraudulent "University" used to bilk hundreds from their money.
3) Set up a Fraudulent Foundation used to obtain tax advantaged money for personal expenditures, and publicly claimed the monies the Foundation spent were charitable contributions and took personal credit for these "contributions".
4) Repeatedly violated a key provision of the Constitution known as the "Emoluments Clause".
5) When U.S. agencies found that Russia had interfered with a U.S. election, he sided with Russia over his own country's intelligence and law enforcement agencies.
6) Drafted a false statement about the purpose of a meeting between his campaign staff and a Russian operative.
7) Created chaos among world trade markets by repeatedly announcing new tariffs, and then days or weeks later extensively modifying his position when shown the damage that would be done to American interests. Then claiming he is a great deal maker!
8) Expressed the opinion that cooperating with Federal prosecutors should be illegal.
9) Hiring foreign agents as his campaign chairman and his foreign affairs advisor.
10) Claiming he would build a wall between Mexico and the US and get Mexico to pay for it. A prima facie absurd, claim.
11) Claiming that Barack Obama is not a native born citizen of the United States. And refusing to alter his position even after being confronted with irrefutable facts. (eventually he was begrudgingly forced to stop this nonsense.)
12) Being an asshole.
13) Claiming that those engaged in investigating Russian interference in the 2016 election are engaged in a "witch hunt" despite well over 30 indictments having resulted, including many Russians, and despite several guilty pleas or guilty verdicts from those indicted.
etc, etc .
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*Condone means to overlook. It does not mean to" approve of ", although the word has been so incorrectly used so often in recent years that it may be losing its original meaning, and may now be assumed by many to mean "approve of". Here I mean it in its correct and original sense.