Earliest Communist China?

What is the earliest that China could plausibly go communist with a POD after the fall of the Empire? Take "going communist" to mean having 51% of Han China under Communist rule.
 
There's a slight chance it could have happened in the late 20s/early 30s, when the CCP and GMD had a united front going and Comintern advisors were helping Chiang Kai-Shek. He of course was never Communist, but if he loses the leadership battle to someone who is...

However, the Communists benefitted greatly from Mao's leadership, and he wasn't firmly in control until the end of the Long March. Mao's ability to communicate with the populace was perhaps unsurpassed in world history. His organizational skills and military strategy were excellent also. Prior to him, most Communist leaders were urban intellectuals who had difficulty connecting with, or even considering, the peasantry, and that was a big factor holding them back. Mao was able to take over China because 1)the GMD imploded from corruption and ineffectiveness and 2) he got the peasants on his side.
 
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