Possible Clues:

• Karl -; Groucho -
• Month to vote for Communist
• 'Das Kapital' writer
• 'You Bet Your Life' emcee
• Karl -, nineteenth century German socialist
• 'Animal Crackers' surname
• ''Duck Soup'' name
• Targets, we hear, for a left-wing politician
• Karl who philosophized about class struggle
• * German currency once, from what we hear