The Democratic Party is a party that functions primarily in the service of capital. Fascists parties usually demand the subservience of the bourgeoisie in return for a sort of patronage system that keeps capitalism in place. I wouldn't really call them fascist on that basis. Beyond the fact that the theory proved to be pretty much a disaster for the KPD and led them to make huge errors in evaluating the conditions in Germany, I find it to be a generally lazy analysis along the lines of equating Communism and Fascism because they both oppose liberals. To be clear, neither social democracy nor fascism are good, and they are both political approaches to try and save capitalism. However, they undertake that in fundamentally different ways, and trying to equate them as one in the same will not lead you to useful strategy on how to combat them. I would argue that the Democrats and GOP are basically both liberal capitalist parties, offering only cultural issues as their dividing line.