I think he failed to get his people loyal to him. To build a cohesive team that would run through a wall for him the way Obama did. I think WE saw the best of Trump - on a stage, in front of a TV camera, but his people saw the worst of him and his ego behind closed doors.
Nearly everyone from his past talks about his lack of loyalty, and I think that played a huge role in the failure of the plan and the stolen election.