The entire premise is wrong.
Militias are far more likely to come to the aid of a beleaguered Trump in the course of a coup attempt.
The Militias are mostly Trump supporters.
The article agrees with you. The article’s assumption was that since the majority of militia members are thought to be Trump supporters, they were expected to fade away after the election of “one of their own”, and yet they’re not. They’re not fading away not because they don’t trust Trump, but because they apparently believe (with justification, IMHO) that there is still plenty of threat to Liberty out there.