"Is it the low unemployment? The strong economy?"
Started under Obama. Goosed by tax cuts that ballooned the deficit he promised to eliminate. It's very possible the bottomless corruption and wholesale giveaway of our shared natural resources is also good for the bottom line on a temporary basis. His own government says the tariffs cost the US economy enormous amounts of money. He's engaged in one of the most socialist programs imaginable - destroying the market for a crop with tariffs, and giving taxpayer money to the davastated farmers to "protect them" fro the consequences of stupid financial policy. You know, the "free stuff" vote-buying Democrats are constantly accused of.
"The terrible shortage of wars?"
1. What shortage? We're still in all of them.
2. ISIS still exists. To the degree that they're weakened, congratulate the people who did the work. All Trump did is pass the buck entirely to the military, which he explicitly promised was not his plan during the debate in the below transcript:
https://time.com/4483355/comma...
To answer your question:
The time he said Nazis were fine people. The time his campaign accepted - documented in an email - an offer of election help from the Russian government. The time he requested election help from the Ukrainian government. The time the Whitehouse used a classified DNI server to hide evidence of his criminality. The time he implied that whistleblowers are committing treason and should be executed. The ten documented instances in which he obstructed an intelligence investigation into an attack on the US electoral system because it hurt his feelings. The time he invented a 10% middle-class tax cut right before the midterms (You know, the "free stuff" vote-buying Democrats are constantly accused of.).
The shutdown. Do you not remember when he shutdown the entire US government over a petty vanity project?
The time he said the USSR was right to invade Afghanistan. The time he gave away state secrets to the Russians. The times he had secret meetings with Putin, and confiscated the translator's notes. The time he tried to abuse National Emergency processes over a petty vanity project. The time he illegally appointed an acting AG. The time he asked that AG to interfere in a lawful SDNY investigation. The time he explicitly told government employees to break the law for a petty vanity project. The time he lied about Chinese interest in trade talks to boost the economy.
Abandoning the Kurds to die and ceding US military bases to the Russians.
The time he selected his own golf resort as the location for the G7. The time he canceled a trip to Denmark because it hurt his feelings when they said he couldn't buy Greenland.
And these are just the things that hurt the US. There are plenty of addition crimes, mini-strokes, mental problems, overt lies, and insane beliefs that would be disqualifying even if he were a competent president.