Why are people upset he was called a RINO? He bailed on the GOP and became an Obama supporter; he was not non-partisan. What is wrong with one (novice) politician (Trump) calling him a RINO? Just because Powell is dead doesn’t change this.
Had Powell remained non-political it would have been different. That would have been understandable but it is not the case.
I don’t think folks are expressing displeasure with President Trump for what he said, as much as the timing “when” he said it.