I'll quote a good Reddit comment from a few months ago:
"You many not realize this, but a massive chunk of his popularity is out of protest to left-leaning bias and circle-jerking. Surely you noticed how his polls seems to go up after every controversial thing he says? You probably also notice how all attempting stumpings (this one included) have no negative effect on him. This might fool you into thinking, "Trump supporters are clearly stupid brainwashed racists, there is no convincing them"... and although for some people that may be true, something different is happening with most others.
They are getting fed up with the ridicule. Normal intelligent people, who's political affiliation would be impossible to determine if not revealed, hear Trump say something like "Build the wall" and think, "Well that's a bit extreme and grandiose, but I do want to do something about illegal immigration" and they put the idea into the back of their head.
Then the floodgates of harassment and circlejerking open wide. The constant media attacks, the personal insults, the constant accusations of racist, xenophobe, misogynist, antisemite, homophobe and any other buzzword in the toolkit. They see liberal acquaintances who may be long time friends posting on facebook, "UNFRIEND ME NOW IF YOU LIKE TRUMP YOU FUCKING IGNORANT RACISTS". So they keep their mouths shut. This continues unbroken throughout the entire election cycle.
Then they start to question the media and the establishment. This is the point of no return. They learn how biased the media actually is, similar to what Bernie supporters are seeing with Hillary favoritism. People start to look even more into Trump and his statements/policies. They may see things that they like. When he says something controversial that they don't support, the most optimistic among them will think "This seems like hyperbole to get people talking" (and realize that Trump has been preaching this tactic for decades). The least optimistic will think, "Even if he is being 100% literal we still have checks and balances so it doesn't really matter."
Meanwhile, the circlejerking still continues. The constant abuse and kneejerk hostility against anything Trump makes people feel like they can't voice their opinion in the supposed land of free speech. They see the media saying "Trump's campaign is over for the n+1th time". Yet they see his rising popularity and know that there are others who feel the same way... the "silent majority" you occasionally hear them talking about.
At this point they recognize that Trump is an underdog. He is standing against very established and strong political forces. He lets people speak their minds without abuse. Every additional media attack, "clever" meme, downvote brigade, personal insult, and Hollywood denouncement just strengthens their resolve. They know their vote has power and they're ready to make the establishment sweat."
TL;DR he's banking on the media going overboard on his statements and people who look into them to go down the rabbit hole seeing him as the underdog and anti-establishment.