Just doing a think from way outside the box...
Imagine if you're the sort of person or group who'd rig an election so that your preferred candidate would win and not the one the people voting want. Then that person comes up against someone who cannot be fought by conventional means - someone who says whatever he "thinks" and while everyone is recovering from the outrage of that, he says something even more outrageous, because outrage lasts as long as the news cycle. The public love him because he isn't a career politician who lies for his politician buddies (because he doesn't have any), and his speak-your-mind policy appeals to the bottom half of the population, which is sick of honeyed words and double-speak. And you lose to him, because you have no way to fight that.
Now imagine that person keeps literally demonising people and groups: Mexicans, women, blacks, the disabled, the Democrats, the media. And then everyone expresses horror because this is the President saying that and that will give licence to some lunatics to target these people...
... but nobody does (except for the guy who groped a woman on a plane because the President says it's okay).
So you're the sort of person who'd rig an election for your candidate and now the things the insane President (who you can't fight conventionally) is saying that seem dangerous are not having any effect.
Do you think you'd conceive of a way to make people think that they do have an effect? Do you think that this kind of person would make the danger that they say would happen when the President talks about Hillary Clinton, Barack Obama, George Soros and CNN as evil actually happen? Would that be a way to fight him, where all others have failed?
Only this does rather appear to be an absolute peach of a gift for the Democrats, having so many of Trump's punching bags directly targeted with bombs...
... but it is a phenomenally dangerous tactic for the an actor on behalf to try on behalf of the Democrats. If it comes out that this is the case, that's the end of any challenge to Trump 2020.