I don't think it's that clear cut. Germany had multiparty system before turning fascist. But in early 30's elections in Germany, the communist and the fascist had combined popularity of over 50% on two elections. These parties could have been under same flag in two party system. It's completely possible that similar autocratic popular vote in USA would have resulted similar shit-show.

Alternatively fascist could have sided with SDP if the communist are too bad. And this time we have over 50% popularity in all of the elections in early 30's.