Earlier quoted context omitted.
And this is specifically on a tweet calling the validity of the election into question. It's blatantly wrong, but he needs his base to believe him when he says the election is rigged.
Hasn't the other side been #NotMyPresient and throwing a tantrum about the validity of the last election? Trump is not a trailblazer in this regard
(b) you'll have to be more specific about what you mean, but the "tantrum" I've heard is that the system as set up over-represents land over people, not that the result is illegitimate. A legitimate result in a badly-crafted system is materially different from claiming the process as designed is compromised.