Making Russia a Good Guy works, but the USA as an "Evil Empire" of a Union of American Socialist Republics?
I would say a limited revolution in 19th century Russia, with a surviving but truncated Tsar and a strong Duma, eventually evolving into a functioning industrialized state with limited Democracy by the time of WWI, and early victory for the Allied Powers.
In America, a Gilded Age that never ends, and a Great Depression that happens sooner and is much worse (we'll assume FDR dies of his polio). The CPUSA was never stronger than in 1935, and without the USSR to destroy its legitimacy, possibly a chance to meld over into a chaotic Socialist Party. The problem is, it would take a Civil War Two (and along English Civil War lines this time) to do it, as the US Constitution would never fit a strict Communist mold. OTL, the Russian Empire had to be pushed to horrific extremes to produce the circumstances for the Bolshevik Revolution. What could cause this in the USA? The Civil War didn't do it, and a race war wouldn't either. So, I don't know...
EDIT: Basically, it would mean turning a 150 year old functioning Democracy and turning it into something of a Stalinist Dictatorship. Freedom becomes inbred over time. Weimar could be destroyed, but the USA is no more likely to start goosestepping than the UK.