i think they would've been capable of coming up with national socialism. But assuming not, then probably an absolute monarchy that changes into national socialism when Hitler takes power. I know it's a long time but not THAT long. Democracy is retarded in any nation that lacks homogeneity and even in homogenous nations there are simply better options
Because NatSoc can do what must be done to solve the Jewish Problem even if the general public are too squeamish to accept it.
For example, if a border wall is required, the civilians can be compensated and relocated if their land needs to be used without Chuck Schumers playing lawfare games and a dozen impeachments to delay and distract leadership.