The timing was a big factor too, it was like only a day or so after the attempt and while everyone was trying to calm down the situation and condemn the assassination attempt so as not to incite any other people for doing the same or reaction to the attempt, and then he goes and says that, it was very against the grain of the moment.
Bit of a [tragedy+time=comedy] but the time hadnt passed yet so the edge was too sharp

Calling for death, even as a joke, is deplorable. And in Trumps case, dangerous. It's one thing to make this joke with a couple of friends, it's entirely another when the entire country sees it - both the crazies that would do it, or the crazies that would shoot them for it.