400 hardened targets requiring at least two warheads each also blurs the line between “counterforce” nuclear strikes, where the intent is to spare the civilian population, and “counter value” , or all out thermonuclear war.
Again, having 400 targets on our homeland raises the stakes too high for any sort of successful outcome for any nuclear armed adversary.
It’s actually considerably more than 400 targets. While we may only have 400 nuclear armed ICBMs, there are considerably more silos that contain dummy missiles (missiles that work but aren’t loaded with a nuclear payload.). Only Russia has the capacity to strike us in that magnitude.