I'd say that if we can't use nukes and that was agreed on, we'd go ape shit with vacuum bombs and design a new one to be ICBM capable. We'd build bigger vacuum bombs, as well.
The tech on subs has improved so much that no sub would make it within 200 miles of US soil. Aircraft would be taken out with the literally automatic missles. They even have missiles that can take out other missiles...but that won't even be a factor.
Against an F-22, even modern aircraft don't stand a chance. The missile systems in even antiquated fighter jets who lay waste to all other aircraft.
Quite literally, all opposing aircraft would be taken out long before there was any visual. It would seem almost like magic and they would accuse the US of having phantoms.
And, through diplomacy, we could convince many of the nations to quickly surrender. It would quickly turn into a war against very few nations, especially after the first day or two of fighting.
I'd say the same about Modern Russia versus the rest of 1940 world, too. However, I wouldn't be surprised if they used Nukes.