I'm not sure it's so simple though. That narrative has a lot of mainstream traction and has assumed a kind of popular orthodoxy. Like, from my perspective, obviously there are good reasons that a popular front doesn't happen in the 1930s - for example, only a decade earlier the SDP had sent the Freikorps to crush the Sparticist revolution! But if you go to wikipedia (from which my friend and a lot of other liberals interested in history and politics get a lot of their information from and generally trust because for some reason they see it as different from other big tech companies), the article on the KDP pre-WW2 only has citations from a New Statesman article about how the KDP enabled fascism by rejecting the popular front and supported dissolving the Prussian parliament