I believe modern ICBMs are not really so defensible against. Perhaps some of the simpler ones like North Korean or Iranian ones. If nothing else, dropping a fas

I believe modern ICBMs are not really so defensible against. Perhaps some of the simpler ones like North Korean or Iranian ones. If nothing else, dropping a fast projectile from space is an easier way to create hypersonic speeds than using an air-breathing engine, and there's nothing stopping you implementing manouvreability into these (and I believe that's what modern ICBMs do at the end). US has missile defence programs but they don't seem like a huge priority in the grand scheme of things (just an amateur defence follower here). The main thing about hypersonic weapons seems to be that others have them and US don't so it better close the hypersonic weapons gap. I suppose you never know where the technology might lead. But for example, during the Cold War, Russia had weaponry specifically designed for destroying US carrier groups, which were thought to be a major threat. Whereas US didn't need such weapons, since Russia didn't have carrier groups. So there can be a bit of asymmetry built in from the get-go.