Hitler is killed in WWI, and the Soviet Union looses the Russian civil war, and Russia eventually goes Fascist. Slightly later on, the Communists loose out in Germany is well. Afraid of the onslaught of fascism, the west supports the Spanish left against France and the Chinese Communists against the Japanese. The Nationalist Chinese are more fascistic and in fact end up a Japanese puppet.
World War II is a more harrowing experience and started with a Spanish, German and Italian conquest of France in a mad attempt to establish a new world order. By 1946 America has nuclear weapons and used them to finally defeat Japan in 1952, Germany falls a few years later.
Europe is in ruins. Communist resistance groups in continental Europe and much of Asia have won prestige from the war. Many people in the west feel that if Communism had established itself in Germany and Russia, the whole war could have been avoided.
The new French government is an experimental communist state, which soon allies itself with a Socialist Britain and Gramsci's Italy. Maosist China is seen as something of a separate movement.
In the 70's, after German independence and the establishment of another Communist state the idea of Marxism has made it over to America. This is so significant that following a schism in the Democratic Party that sees many of its members joining a wider Socialist alliance, the CPUSA breaks with the traditional two party system and gets a president elected once.
This president finds himself opposed by a strong Republican legislature and supreme court. After four years, he looses power. Allowing the Republicans to enjoy five uninterrupted terms in office before finally being defeated by a new Libertarian Democratic Party.
Kind of ASB. I think I could do better. Hmm.