This one is a dead loss, not only because no one has found the quote but also because I can no longer identify it. Alan Bates said it in a Steven Seagal movie (Bates must have been desperate for work), but I'll be damned if I can remember which movie. IMDB's two-matching search used to be helpful but no longer is. So let's just forget about whether Hitler was crazy or just stupid and instead go with:
"But can we beat the rap? That's the rancid test!"