If Britain is a willing Axis partner (under Mosley or something), and the RN is reinforced by the IJN, then the USN has a tough slog. After (if) the USN defeats the Axis navies, then the US Army gets a reverse 2000-mile SeaLion... I have a TL on this on another site, actually.
Mike Turcotte
Hmm, was it Last Defense: America Alone Against the Fascist World?
The best chance for a tapped out America personally?
It was a total bitch to take on. It got until 1971 and the only liberated country? Great Britain.
Of course the fact that the Kriegsmarine was non-existent by then and there were 23 USN supercarrier-led battlegroups roaming both oceans, well...