Sure, the Republican primary electorate found Trump compelling, and that's why they won. And that's what scares me. I don't think they necessarily should have found any of the others compelling (what an awful field of candidates, I mean, seriously, what happened there?) but that's beside the point.

In 2000, Bush mainly kept his mouth shut. But Gore's campaign manager made a series of public statements along the lines of "Gore has clearly won, and if this goes to Bush it's a travesty of the election." That didn't help heal or unite the country after the election; arguably, the division has remained ever since.

Trump could do the same thing, but do it much more loudly, bombastically, and in a more attention-grabbing way. The only prevention would be for him to lose so strongly that nobody listens, and everyone writes it off as the whining of a bitter self-deluded loser.