The response below is a good start. Read it. It's dead-on.
But to add on a couple of those points:
1) The 100% no-going-back deal-breaker was January 6th, and the relentless cascade of lies, INTENDED TO DESTABILIZE THE COUNTRY, leading up to it. January 6th was an attempt to overthrow our government. It was urged on, supported, and actually embraced by Trump. He betrayed our country, he stands by that betrayal, and he continues with the same lies, further dividing and destabilizing our country. You are either the president of the entire country, or you are not fit to be the president of any of it.
2) He is a stochastic terrorist. He says horrific things about those who are weaker/smaller/less advantaged than him, intending to and actually inciting violence against them. A slaughter in an El Paso Wal-Mart. A massacre in a Buffalo grocery store. A mass murder in a Pittsburgh synagogue. Horrific slander against Haitians in Springfield. When he calls people with names like mine "murderers and rapists," not only is it false (native-born people commit violent crime TWICE as often as immigrants; that is, you are statistically MUCH safer if you are in a room full of immigrants than you are in a room full of native-born Americans), it incites violence. He knows it. He does it on purpose. He LIKES IT. He is a terrorist, in every sense of the word.
3) His lies are relentless. It's not just "nasty talk." It's psychotic, and pathological. There has never been a figure in American politics anywhere close to the level of liar that he is. We're not talking the "everyone fudges here and there" -- he lies about the most obvious things.
4) He sides with our enemies. All of our allies are aligned against Russia and its horrific invasion of Ukraine. He sides with Russia.
5) He does not actually stand for anyone but himself. You suckers think he stands for your side of the political aisle. No. He does not. He doesn't give a single iota of shit about you. He only cares about power, and trying to fill his internal void with power and approval. He can never fill that void.
6) I have 30 years of experience working with large enterprises. I have seen hundreds of executives in action, and their level of competence covers the waterfront. Some are amazing leaders, the top 5% able to accomplish incredible things deftly and brilliantly. Most are in the middle 90% - good enough, sometimes hitting the mark, sometimes missing it. And then there is the bottom 5%, which is people who are genuinely incompetent, narcissists, idiots, etc. And truly, there is the bottom of that class. The bottom 1%, who are malignant, who come in and make everything about themselves, who lie, who cheat and break deals, and do incredible damage to the enterprise. I know executives, I've seen Trump's type before, multiple times. He is a cancer. BTW, I was livid when Bill Clinton wagged his finger and lied to me. I still hold him in contempt for that. Trump tells more lies in a week than Clinton told his entire presidency. If you thought that Clinton's dishonest character was disqualifying then (and I did), the you cannot think any differently about Trump today.
7) Want proof that he is a cancer? He is a completely failed businessman. He has not succeeded at any legitimate business -- he has only tread water, starting with a fortune, and keeping pretty steady (the return on his investment is less than what it would have been if he'd have just dumped his initial stake into the S&P 500). He is good at one thing: selling himself. He is con-man and a grifter. Again, I've seen more than a few people (almost always men) like him. The only thing remarkable about him is the scale, that he managed to go national with it.
8 ) His bizarre and inconsistent "economic policies" that he has promised this campaign are nothing but 5th grade class president-level promises of "recess all day, no more tests, and free ice cream in the cafetaria." TWENTY THREE Nobel prize winning economists have pointed out that his proposals, if implemented, would be disastrous. And it's obviously so.
9) He is a weak, not very smart man, who allowed himself to be completely manipulated by the worst elements of the Federalist Society to appoint judges who flatly disregard the rule of law (at best) and often do that AND are incompetent (they were selected because of their loyalty and malleability, NOT because they are qualified). As someone whose livelihood is closely tied to the skill and performance of the men and women who wear black robes, I have seen a rapid decline in the quality and ethics of that group. I now have to advise clients things like "I don't know what will happen here, because this judge is just not smart." Or, even worse, "I know what the law is and says, but this judge is going to do whatever the Freedom Eagle Religious Institute amicus brief tells him to do, so buckle up."
10) Decorated men, who took an oath to serve their country, and take that oath very seriously -- think men like Mad Dog Mattis, who (before he came out and spoke the truth about his view of Trump) MAGA ADORED -- have flatly told us that their experiences with Trump informed them that he is an existential threat to the Republic, and he cannot be allowed to take power.
As to anything Trump has done that I approved of? Fuck if I know. I'm sure he pardoned at least one person who probably should have been pardoned -- somebody convicted of a drug crime or something.