Stalin okays earlier alliance between Communists and Social Democrats

Stalin criticized social democracy as "social fascism" and prevented an alliance of the broad Left in Weimar Germany. If Stalin gives the go ahead to an alliance earlier, when he sees the rise of the Nazis starting with 1930, does a coalition between the two prevent Hitler from coming to power? And if such an alliance works temporarily, what becomes of it if it succeeds? I assume they would turn on each other rather quickly.
 
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