If this is, as you say, “a closer case than most” then (as another has pointed out) what of other cases where Trump went further in encouraging violence? Such as the time he promised to pay legal fees? Or when he lamented the good old days when a protester would be taken out on a stretcher as he belittled police efforts at control?
In this case, and in other cases, Trump’s words encouraged violence that did happen. In some of the other cases his words pushed things even closer to the legal standard you discuss than this case did.
Of course, all of this misses the most concerning point of all. This is the President of the United States acting like this. It’s the President of the United States pushing legal standards for encouraging violence from his followers. Whether legal or not this is conduct repugnant to the office in which he sits.