Minimal Divergence / Threshold for No Red Scares

The challenge is to propose the PoD - after November 7th, 1917 - which prevents any Red Scare from happening while causing the least divergence from OTL's 20th century otherwise.

How much, or how little, do either the Bolsheviks / Communists or the US administration and public have to change to achieve this?
 
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