Even if he is incompetent, you get him lying under oath and he's guilty of perjury. The penalty for that may be prison, or he may plead insanity and the penalty is involuntary commitment. Judges do not take kindly to lying in court.

And Trump thinks he's packed the courts with "his guys". But what he's done is packed the courts with conservative judges nominated by The Federalist Society. They tend to be the strictest when people bring BS legal theories to court and then lie about them.