He should have kept his mouth shut, but I think there is virtually no limit to what technology can do.

It's in the best interest of the US to have a fully working nuclear shield working, but in such a way that almost nobody knows about it. Depending on the level of technological sophistication, it's probably possible to make a global working nuclear shield with just a hundred people even knowing it exists with just three or four that know the operational details. It's even possible to reduce that number to zero in principle, although that would not be recommended and you would have to shoot everyone with knowledge of the project.