Can't see the CPUSA calling the shots either. For the USA, the only way for Communists to get big to win elections would be a far more successful fully unified Farmer-Labor Movement Party, that would be far more ‘anarcho-syndicalist' than Communist, and the problem that this group really had little use for the Communists, and that's before Stalin took over.
Once Stalin got into power the Soviets would back the CPUSA to throw out the other factions. They tried that in Republican Spain, and did very well.
And the Organs of State Security (the GPU-OGPU-GUGB and the Razvedupr-GRU [they changed names]) would be working covertly to secure power. The security services of the communist America would be focused on suppressing capitalist, religious, and other opposition, not their fraternal allies.