Trump denied his 2020 loss, prevented a peaceful transition of power, then incited an insurrection in which people waving Confederate and Nazi flags attacked law enforcement, attempted to gas legislators, and expressed the desire to execute by hanging Trump's VP Mike Pence.
He treasonously stole classified documents and then tried to cover it up while maintaining that he is above the law (which is heretical to the rule of law in constitutional republics). His children secured multi-million business deals while working for his administration in violation of Foreign and Domestic Emoluments Clauses
His inability to process information or tolerate learning important details - as testified to by those who served in his 1st administration - is immensely less than what the highest office in our nation requires and deserves. His mishandling of the pandemic led to 400,000 excess and preventable deaths. He expressed his wish to bomb a hurricane with a nuclear weapon.
He is sadistically cruel; mocking the disabled, mocking combat-wounded veterans, bragging about sexual assault, spreading thoroughly-debunked racist propaganda against non-Whites, and retweeting and amplifying the rhetoric of White Supremacists and Neo-Nazis so carelessly the Holocaust memorial groups have had to speak out against him. He used hate speech and tropes which echo those of Adolf Hitler and other Nazi's.
He habitually degrades women and had tried to pay off an adult film star in the effort to cover up adultery he committed during his 3rd marriage, and managed to commit federal campaign finance law while doing so.
He routinely violates national security laws and protocols in dealings with authoritarian foreign leaders. He has repeatedly threatened to violently use the U.S. Military or the domestic terrorists groups he tells to “stand back and stand by” against U.S. citizens who his narcissistic ego feels are “his enemies” or have dared to oppose him.
He has threatened mass deportation of refugees, asylum seekers, migrants, and even naturalized citizens. He has threatened to deny LGBTQIA people their civil rights. Both of these threats are in direct violation of the constitutional precepts of The Rule Law and the Equal Protection of Rights.
This section could literally go on ad infinitum, but you get the point.