If the United States enters the European war in 1939

How much changes if the United States enters the European war in 1939 or 1940?

France probably does not fall, American industry supports the Allies immediately, and Italy is unlikely to enter the war.

The immediate American field force would be limited, but industry and supply would be committed without the later restrictions of Lend-Lease. More importantly, France would know that another great power was fully engaged and would have less reason to seek an armistice after a German breakthrough. Italy, which historically entered only when France appeared defeated, would probably remain out.