Investigate the potential to develop a global Anti-Ballistic Missile shield.
A system whose purpose is to intercept ballistic missiles during their boost phase. An example (written in 2018) of found online is:
Likely a different design, but conceptually a constellation that could serve as a “global shield” to protect against even a medium-scale exchange. The “protection” could be extended to cover ballistic exchanges - even protecting smaller states (even those not friendly to the USA) from rogue actors.
In theory, major states (US, China, Russia) could coordinate on some aspects of a constellation… so it is clear it is defensive in nature… maybe permit some “inspections” prior to launch.