I’m not in the US, but it seems to me that the Republicans keep breaking norms and procedures, including politicising impeachment and ignoring illegal, immoral and plain bad conduct.
They also seem to be fine with not applying the same standard across the isle.
On the other hand, either Democrats follow new precedent, with even more devolving, or they keep the old decorum and get their asses kicked by Republican foul play.
What ways out of this spiral are there?
It is not possible at all. No one familiar with German law and culture think this. This is not a talking point I have ever heard discussed seriously. There ist probably hundreds of reasons why it could never happen. Our legal framework ist very strong and we have a strong civil framework of resistance in case something goes in that direction.