>On the same note, the German communists were quite strong, and at some point they were surely stronger than the Nazi party. Unfortunately, the rigid hierarchy of the movement at the times (read: Stalin's dictatorship over the movement) found that there were more important enemies to fight at the time. The Nazi party had the "socialist" word in its name after all, and eventually the Molotov-Ribbentrop pact sealed the policy: communists didn't dare try anything against Nazis between 1939 and 1941, and by that time they weren't to be seen anywhere. It's not a coincidence that a communist was framed for the burning of Reichstag - at that time, they were still a threat to the new regime.

The KDP (German Communist Party) was strong, but never as big as the Nazi party - 350K vs. 1.2 million. The 1933 Reichstag fire was used as the excuse to finally crush them. They didn't dare try anything after that, simply because their leadership had been wiped out.

(http://en.wikipedia.org/wiki/Communist_Party_of_Germany)
(interesting theories at http://www.che-lives.com/home/modules.php?name=News&file=article&sid=111)

update: http://www.spartacus.schoolnet.co.uk/GERkpd.htm has a table showing KDP representation in the Reichstag from 1920 to 1933. The only time they out-represented the Nazis was in 1928.