I think I also read somewhere that a lot of our nuclear stockpile has decayed to subcritical levels and can't actually detonate anymore and we're not sure how much of it is in that state

EDIT: No single source, on further research it appears that the cores decay in unpredictable ways that can affect how they explode, and the program for recycling them isn't running properly and we can't do underground nuclear testing anymore to check samples of stockpiles so they're kind of in the dark on which ones need recycling. If anything it's the hardware in the warheads themselves that will break down faster over time and since it's the United States of America maintaining the warheads they're overbudget and behind schedule and not even sure which warheads need maintaining first.

Regardless the technology for shooting down missiles has improved a lot since the end of the Cold War so hopefully if anyone is insane enough to actually launch missiles they'll be destroyed before they can cause any damage