What is it about Trump that has allowed him to acquire so many ardent followers?

[Alan V]

And now that we’ve got radicals who have long been alienated from the political process actually having a candidate to root for (and he doesn’t even need a coherent ideology; it just needs to be extreme enough that they can project their own hair-brained ideas onto him), it only makes sense that they start up a cult of personality for him, and due to his slapping his name on anything that would pay him, a lot of the structure for that’s already in place.

Interesting video.

After Obama beat Romney, Republicans did a post mortem which told them they needed to move back toward the center to appeal to a wider range of voters in the future. Trump turned that on its head by doubling down on the base in a way which shouldn't have worked, but did because he appealed more directly to the fringe elements of the Republican party which had been shut out previously. That helped to make up for the deficit identified in the post mortem.

It also helped that Clinton was a weak candidate, that Comey's public announcement was poorly timed, and perhaps that Russian propaganda demonized Clinton as well. Conspiracy theories have a way of appealing to the bigoted and marginalized.