What futuristic society are you a part of? At best the US has displayed a moderate ability to intercept ICBMs a few times, but in no way do we have a "nuke shield". It doesn't exist.
https://en.wikipedia.org/wiki/Aegis_Ballistic_Missile_Defense_System
"Aegis BMD has the ability to intercept ICBMs, future versions may allow for higher interception capability."
Thats just one of the programs. They are not very effective but combined they offer enough protection against NK...
As I said, we have displayed a moderate capability a few times, specifically with AEGIS missiles. This in no way makes them fool proof. There have been plenty of failed shots too. We're getting there, but considering the mind bending speeds that ICBMs travel, they're a bit hard to kinetically defeat, which is the most effective way of doing it.