Despite public sentiment against involvement in the war and a substantial isolationist segment of elected officials, FDR and Congress did take some steps toward preparation for the eventuality of war. In the latter stages of the New Deal programs two aircraft carriers were built as part of the legislation. The Virginia National Guard and other state guards were mobilized for a year of duty in early 1941. Congress passed the Selective Training and Service Act in 1940, the first conscription in peacetime. Modern aircraft like the B17 and B24 were already on line, even if not in large numbers, by December 7, 1941.

In other words the president and the Congress were not in denial about the existence of a threat and were making plans to deal with it. To your point, it would be another year, at least, before the US became the Arsenal of Democracy and the US Navy and the US Army were large enough and experienced enough to make major offensive contributions to victory.