Who/whom ate my sandwich?
Try substituting “she” and “her”: She ate my sandwich. Her ate my sandwich. “She” works and “her” doesn’t. That means the word you want is who.
Whom ate my sandwich?
Who ate my sandwich?
Let’s look at another:
Who/whom should I talk to about labeling food in the refrigerator?
Try substituting “he” and “him”: I should talk to he. I should talk to him. “Him” works, so the word you need is whom.
So back to your question, since "him" fits President Trump better than "he", the word you need is WHOM.