Assassination is wrong. But any clever assassin planning to ultra-secret assassinate someone like him would make it a character assassination as well: overdose in bed with a prostitute, or similar. Anyone with an ounce of political sense would know that shooting him in public would only motivate his base.
This is strong circumstantial evidence that he was killed by an individual who suffered from a mental health issue. Thoughts and prayers, we need more mental health support in our country, and of course, gun regulations to keep people who might snap from having guns readily available.