The concern is he could
What would stop him from initiating something like this? He can certainly try either through his own cable channel (which he has said is not going to be created) or through some other kind of organization. His ability to do that would depend on just how aggrieved persons might be and how strong Clinton's hand is after the election.
A landslide for Clinton would certainly help. A watchful eye from Pres. Obama would be essential. And a vigilant public alerted to possible trouble from Trump would be critical.
Trump Threat Not to Accede to Clinton Win Mostly Hollow