Trump's inciting his supporters to violence reminds me of a quote from the philosopher Karl Popper.

[Jim Lane]

11. American law is more protective of free speech, and properly so, IMO

A majority that's unhappy with what's being said would have a lot of leeway under Popper's formulation:

We should claim that any movement preaching intolerance places itself outside the law, and we should consider incitement to intolerance and persecution as criminal....

If a Louis Farrakhan says in a TV interview or writes in a pamphlet that the white race is a race of devils, that speech could readily be criminalized in any jurisdiction with enough jurors who are offended by it. The same would be true of a Stormfront website that preaches intolerance but in the opposite direction.

In modern American jurisprudence, the First Amendment isn't an absolute, but the bar for suppressing speech on such grounds is pretty high. The Supreme Court has used different formulations, but they amount to variations on the "clear and present danger to public order" test. If someone is carrying a "Dump Trump" protest sign at a Trump rally, and Trump says from the podium "Let's rough that guy up!", then arguably there would be such a danger. If the feared connection to violence is less direct, however, as with Farrakhan or Stormfront, then the speech should be permitted.