One thing not being taken into consideration in all of this is logistics. The key to any war, finance, food, productivity, and supply lines. Bear in mind this whole theoretical war would rely upon Europe getting along so it is assumed as the basis of what Im writing.
Europe has a large amount of untapped oil both on land and at sea. Financially Europe is in much better shape. Europe has superior health care (manpower). Europe has more fertile land. Since Europe comprises of many independent nations, manufacturing is also harder to interrupt as most of them have self contained industry.
America's only advantage would be supply lines. Organising a singe republic, V's dozens of independent nations is far more efficient.
Americas biggest enemies? a huge coastline, a lack of allies outside of Europe, reliance on imported oil. The war is lost before standing forces are even taken into account.