Like a hurricane projecting so many joules of energy into an ocean of assholes, that their obnoxious storm surge washes away more credible, but presumptive opponents right of center.
He'll never win, and that's the point.
One way or another, these conspiracy-theory explanations seem a bit counterproductive from the perspective of any of the actors who might reasonably have carried out the conspiracy. The simpler explanation – that Trump is an egomaniacal bully with little knowledge of world affairs, and that enough Republican voters tend to like that for him to honestly win the primary against a weak and crowded field – seems more plausible to me, but hey...
Sadly, everything creates its own reaction: the rise of a black person who contradicts all the negative stereotypes merely enrages those people for whom "white" is an important part of their identity. See also people getting angry about female Ghostbusters.
The republican party spent so long sending coded racist messages to their supporters that those supporters have forgotten that they were supposed to speak in code.
Oh come on. From the reviews leaking out it sounds like Ghostbusters is a legit shitty movie. A spoiler for the ending is out there; go read it and tell me this isn't something a 5th grader would write. No, I haven't seen it, and I probably won't, and it has nothing to do with the fact that it is a female cast, but because it doesn't sound like something, based on the trailers and previews, that I would willingly spend money on.
No one complained when the main protagonists of Star Wars VII were a woman and a black man. (Or did they? I don't know, I certainly don't remember hearing it if they did.)
To be fair, even without that control mechanism, the DNC arguably is less vulnerable than the GOP. While both parties have state-to-state variation in how delegates are selected, the DNC uses basically proportional allocation in every state, whereas the GOP uses heavily disproportional mechanisms in most states (to the extreme of winner-take-all in some), which allows an early plurality in a crowded field to turn into commanding delegate lead (this seems to be by intent; its expected that connected insiders will have an early advantage, and this setup is would then get the primary competition over quickly and give the party more time to focus on the general election -- but its also easy to see how, with widespread dissatisfaction with party elites and an outsider candidate with strong name recognition and the ability to score early free media, it can backfire.)
I mean, look at the 'wall' proposal: it's a nice simple authoritarian solution which people who are afraid of Mexicans taking their jobs can support. And he even promises to get foreigners to pay for it!
None of this is remotely feasible, but that doesn't matter, because the "reality-based community" is passé. (https://en.wikiquote.org/wiki/Karl_Rove passim)
None of the other Republican candidates could attack him for racism without alienating their voters, because for years they've been obliquely signalling their approval of racism. None of them could attack him for not being realistic without suffering the same problem themselves.
None of the political candidates are fundamentally disagreeing with Trump. They mostly believe that illegal immigration should be stopped and that legal immigration is perfectly fine.
The primary thing that separate Trump from either the Republicans or the Democrats in this discussion is his choice of words not his agenda.
Even Hillary was for building a wall at one point.