The Soviet Union still enters a shorter European war

Even if early American entry prevents France and Norway from falling, the Soviet Union cannot remain neutral indefinitely because Germany and the USSR still view each other as existential threats.

Question

If the United States enters the European war in 1939 and France does not fall, does the Soviet Union stay out and change the postwar settlement?

Short answer

Probably not. The USSR still intervenes against Germany, although the stronger Allied position may cause the German economy and war effort to fail sooner.

Notes

Avoiding Barbarossa would not necessarily keep the Soviet Union out of the conflict. If Germany did not attack first, Stalin would still have reason to enter before the Western Allies settled the war and forced Soviet concessions in Poland. At the same time, American participation would make German victory in France and Norway far less likely. Continued Allied access to Norway would threaten Swedish imports, while the unchanged western front and Italian neutrality squeezed Germany's economy. The likely war would be shorter, but Soviet intervention would remain part of the strategic calculation.