The thing is, if we elect a criminal king, the US is toast too.

Is it? Again, your thesis for electing a person who has terrible policies instead of the person who has committed a crime is that we'll be able to undo the damage of their four years. Why wouldn't that similarly apply to someone who was just personally terrible? It seems to me that if we elected a bank fraudster as President, but he mostly pursued good and beneficial policies, that it would be worse than having a non-bank fraudster as President....but not mean the U.S. was toast?

As for the Congress, the Presidency is important enough that even without having a trifecta it's still really consequential which party holds that office. They then get to control every judicial appointment, every policy decision from the executive, all foreign policy decisions (for the most part)....for four years, and in a lot of areas where the effects will linger for quite a long time.