Unconventional though he is, Trump would not endorse his supporters protesting violently. As evident from his TV address telling them to go home peacefully. The question, is why are the protesters so worried about Biden winning, and why is Trump convinced he won?
If one million remainers can protest outside parliament, the actual protest of Trump's supporters is not unusual. The violent aspect probably didn't originate with Trump but others.
I voted Leave but totally support the right of remainers to do what they did, this is not the same.
Why is Trump so convinced he won, he would be, were in not for the US Constitution, the US version of [insert choice of most notorious dictator here].
I've said this on this forum, before the casual demonisation of politicians is very dangerous because when the real demons emerge they can actually thrive!