Also, here's another reason Hitler is unlikely to come to power in TTL...
In OTL, Stalin forbade the German Communist Party from cooperating with the Social Democrats to stop the Nazis.
Trotsky or some other non-Stalinist leader might not be that shortsighted. In TTL, the KPD, SPD, and other non-Nazi parties might band together to keep Hitler out of power.
Undeniably Third Period Stalinism (the period when the Communists acted under the assumption that the "social fascists," i.e., the democratic socialists, were the main enemy, not the real fascists or Nazis) was a bad and stupid policy. But would an alliance of the Communists and Socialists have been able to stop Hitler from coming to power? The top people in Germany and a huge petty bourgeois and middle class pro-Nazi movement, with Nazis having thoroughly infiltrated the military and police, would have burgeoned even more rapidly if the Right had perceived a really effective and united left threatening to outflank them. And this united left might actually have been a paper threat: Look at what happened after the end of the Third Period, when the Communists adopted the Dimitrov policy of a united front and popular front against fascism. These "fronts" were completely ineffective anywhere. Leon Blum's France did nothing effective to stop Hitler or Mussolini or Franco or to prepare France for World War Two. So I would guess (nobody can really know) that a Communist-Socialist alliance would not have stopped Hitler from coming to power, and would have been crushed in the street. If the left had then tried a policy of armed civil war, the other side would have had the guns. And if the left began to get some guns (we're talking about 1931-33), following Trotsky's prescription to just steal the guns from the factories where they worked, or from railroad boxcars, then the British, French and Italians would have actually encourage the German military to crack down hard--and with what result? They crack down on the socialists and communists, but not on Hitler. He waltzes to power. Maybe.