Except self-defense, when the motive of the intent to kill is highly relevant.
Dersh did much better when he referred to the case. Trump could have a pure motive, only national interest, or only an impermissible motive, graft, of a mixed one - something for the country and it happens to benefit him. This is the most common situation for all political decisions, but even if not (made up examples of Obama refusing to use force in the national interest in order to appease leftist voters), still not impeachable.
I'm just saying that it wasn't relevant to Dershowitz' answer, and in the interest of time he didn't dwell on it but acknowledged it.
Trump isn't on trial for shooting someone on 5th Avenue.
-PJ