If it's anything like religious "Great Awakenings" that the US seems to go through every now and again (which I think it is), I think you'll find the movement much smaller than it first was as people on the fringes peel away quietly with each disappointment. They didn't lose anybody for years because they didn't really get to be disappointed, but now they have their promised messiah back in power they're struggling to make sense of it all. The core might double down after each disappointment until the leader dies, but each time they have to add a new layer of complexity to what they believe, and each time they will lose a few people, particularly people that find the least community and identity through the movement. People that won't lose as much if they leave.

Where at the peak of some "Great Awakenings" the majority of people are part of the movement, by the end it's sometimes just a small community of a few thousand members. There is never a single event that causes most people to leave, it's gradual.

Edit: I'd also like to note that they didn't have much opportunity to be disappointed in his first term (most of the terrible things he did didn't really disappoint his followers) until the end when people were dying and inflation was rising, but their messiah was out of power before they saw the full effect of it, and so they got to blame somebody else for inflation and Covid deaths and so on (if they even believed Covid existed).