He didn't start out that strong, did he? Among the conservatives I know, his true supporters that have been with him from the very beginning haven't changed. And of the ones he's gained, they're only jumping on board, because they think Hillary is the more corrupt. I got to listen to a whole speech just yesterday by a co-worker in the breakroom when he glimpsed Hillary on TV about how "It's a sad state when Trump is the better option."
But all of the true supporters of his that I know supported him from the beginning, and are people with latent aggression bubbling and building pressure under the surface of their persona, waiting for release. My own boss is one of those people, and I think the reason she's a manager is because she absolutely gets some sick relief from verbally assaulting people. There's something that burns constantly deep within her, and to mercilessly chew someone out or humiliate them is like a soothing balm to that pain. Being the boss gives her the opportunity to do this on a regular basis with legitimacy. When she's in a bad mood, she will skulk around the office just looking for somebody to give her something to pick on for that release. This is a true Trump supporter.
People who are loud and proud about being of this nature are like beacons to their kindred. They make each other feel validated for being who they are, and empower and embolden each other to more openly unleash their aggression on a broader range of others. And when they band together like this under the right circumstances, they dominate their environment by cowering others into pretending to join in to avoid being on the receiving end.
I'm not saying that 40% of the U.S. is like this, but my opinion and personal experience (life in Indiana and observing what's glorified by our media) is that this type of persona enjoys a lot of success here.