Check your history. The United States did not enter WWII in Europe until Germany declared war on the U.S. on December 11, 1941. Russia had been fighting the Germans since June 22, 1941. The U.S. and Russia were on the same side the entire time the U.S. was in the war.
Lend-Lease convoys to the Soviets started August 1941 well before the German declaration of war on the US.