Checks like Congress, a majority of which is terrified to stand up to him even after an attempted coup and comically bad cabinet appointments?
Or the courts, many of whose judges he appointed and shamelessly render verdicts (often on his behalf) without recusing themselves over conflicts of interest?
Or the executive branch, of which he is the head, and can cycle department heads like an episode of The Apprentice?
> He was president once, and was not able to pull off a successful insurrection, or murder any political opponents
The US passed an entire amendment to its constitution to prevent insurrectionists from repeated attempts to take over. The fact that he attempted to do so is already treason. One doesn't have to succeed to be disqualified. Otherwise what's the point of the amendment? Just keep trying until you succeed.