It's worth pointing out that Trump's videos yesterday -- praising the people who had just attacked and sacked the Capitol Building during a joint session of congress and conspicuously refusing to demand they leave -- were probably legally an incitement to violence regardless. Certainly normal prosecutors could get convictions on that sort of thing[1] in normal courts. The only reason it seems gray is because the speaker is the President.

[1] Remember that in context they were at the capitol because Trump himself, in person, had directed they march there just an hour before. I mean, really, that's pretty open-and-shut as far as mens rea.