This deeply misunderstands the Court. The legitimacy of the Supreme Court rests not simply on the justices being placed on the Court via the letter of the law, but also on the Court being an impartial arbiter of what the Constitution says. With verdicts like Trump vs. USA, the Court (especially certain justices) has pretty well jettisoned even trying to convincingly appear to like a judicial body and instead is behaving as a purely political actor. The Court has never been immune from politics, but its legitimacy rests in restraining itself by what the Constitution says, even when the justices don't like it.