On other sites, Trump supporters have been saying they're going to string up Hillary once Trump wins. That wasn't an isolated comment; the sentiment comes up often. Granted, it could be that when I see it, that I find it to be extra-memorable. And maybe these are the freaks who think they've found a voice in Trump and so now feel empowered to say things they wouldn't normally say, which means that once he's gone, they'll go back to just being less vocal assholes.
But violence is a real possibility, particularly if Trumps keeps up this bullshit about the election being rigged. The problem is to the extent with which Trump actively encourages the behavior. I briefly re-looked up Incite to Riot, but the cases are all over the place and federal interpretation varies (meaning that different circuits have treated it differently depending on circumstances).
Thus far, he has not been able to keep his mouth shut. But it's doubtful that not actively discouraging his followers from rioting is a crime. It appears though, that if he actively urges or encourages it, he could get himself into trouble. Anything short of that will likely be protected speech and it would only make him a martyr to arrest him and put him in jail.
But he could get himself in trouble in other ways as well could his followers.
1. Insurrection: an insurrection may properly be defined as the act of rising in open resistance against established authority or government,1 or as any open and active opposition of a number of persons to the execution of the laws of the United States of so formidable a character as to deny, for the time being, the authority of the government, even though not accompanied by bloodshed2 and not of sufficient magnitude to render success probable.3 It need not take the form of an attempt to set up a new government by name. 4 While an insurrection aimed at accomplishing the overthrow of the constituted government is no less an insurrection because its chances of success are forlorn,5 it is necessary that the rising must be so formidable as for the time being to defy the authority of the government.6
Insurrection may also be defined as a rebellion,7 or an armed rising or revolt.8 It may further be defined as a rising against civil or political authority,9 or the open and active opposition of a number of persons to the execution of law in a city or state.10
2. Sedition: "Sedition" may properly be defined to be a revolt against legitimate authority.13 It may also be defined as the advocacy or suggestion, by word, act, or writing, of public disorder or resistance to the government.14
So Trump needs to be careful, a thing he hasn't been disposed towards at any time in the past year and a half. But there's still the martyr problem. Trump would become a perverted version of Nelson Mandela to his most idiotic followers, and would inevitably lead to various acts of domestic terrorism by benighted dipshits all across the U.S.