They should have called him deplorable. I'm sure that would have convinced Trump supporters that he's no good.
They weren't trying to convince anyone of anything. They didn't know they were on the mic. They were just laughing at Trump's antics. No need to make it into more than it was. You'll get through this.
But you're right about Trump supporters. Trump could take a shit in the middle of the floor and Trump supporters would call it genius.