Trump is a very effective president for the GOP, as his antics gather a lot of attention and take attention away from policies the GOP puts in place that would not withstand public scrutiny. That's the good side, tho I don't think it so as a liberal.
His ""horribleness" has two aspects, the personal and the political. On the personal side, he called Mexican migrants "rapists," offering no proof, he has insulted women's looks, he is a shameless narcissist and an extraordinary liar about things big and small. He said a judge (Curiel) could not do do his job because he was of Mexican descent, something Paul Ryan called textbook racism. He spread false info on black on white homicide. When the Central Park Five were exonerated by DNA and successfully sued after a cumulative total of 40 years in jail, he didn't have the decency to apologize for his lynch-mob like ads he placed in NY papers calling for the death penalty for them.
On the political side, a scattered list from my scattered memory: he appointed Betsy DeVos as Sec of Education... Never a teacher, a principle, a school administrator. He violated US and treaty law with the way he treated migrants from Honduras fleeing drug gangs, never mentioning why they may have fled, and falsely saying their were "Middle Easterners" among them, readily admitting he had no proof of that, but no doubt said to increase people's fears. He came to office with significant support from white working class people, yet his administration eliminated the requirement that US officials consider deaths and injuries on the job when awarding government contracts. His administration legalized a pesticide that causes birth defects. He claimed that the world was laughing at the US, but his first words to the UN were this past fall were greeted with scornful laughter from the world's representatives. His comment on a major climate report by his own administration was, "I don't believe it." He said he would eliminate the deficit and debt, but this year's deficit may set a record. He has expressed admiration for the murderous tactics of Iraq's Saddam Hussein and the Philippines Duterte, as well as other dictators, while attacking democratic allies. His attacks on the press as "enemies of the people" quotes one of the great mass murderers in history, Stalin, and have been taken up by others.
That should do for a start.