Given the type of both recent and predicted conflicts that the US has been involved with, it's not 100% clear to me that the US needs yet another aircraft. That is, fighting in proxy wars or fighting in countries like Iraq, Afghanistan, or Syria don't need anything new. And fighting a sophisticated enemy would probably ramp up to nuclear deterrents and diplomacy anyway...fighters wouldn't make a notable difference in that kind of war.
Won't happen, but it seems like they should just buy fighters from allies where the F-35 isn't a good fit.
China, so we can defend Taiwan without having to go nuclear to do it. Russia, over the rest of the Ukraine. Perhaps Iran, if we have to stop their nuclear program by force, or some other contingency.
It doesn't escalated because neither Moscow nor DC are willing to go nuclear over Tallinn while Beijing is overwhelmingly inferior in their nuclear capability compared to either.
I don't know that we have a good historical example to confirm that. I remain skeptical that we could have direct fighting between American and Russian/Chinese soldiers/aircraft/etc and somehow keep that in a box. The Cuban missile crisis was insanely tense, and no real shots were exchanged.
One could argue that is the precicely the problem.
If there is no specific credible enemy to fight, there are no strict reguirements that MUST be met, so one makes the plane do everething, because you dont really know what you need.
Won't happen, but it seems like they should just buy fighters from allies where the F-35 isn't a good fit.