3) they can see if any countermeasures would be effective
4) they can figure out what to look for and find those weapons before they're fired
cfr. nuclear deterrence, right. There is "nothing" the US can do about other nations enriching uranium and making bombs, other than bombing those countries. The US can't change the laws of physics, follow the right formula and it'll work. However the US can figure out exactly what to look for to either prevent it from happening through intervention or at the very least get some warning before it's used ...
How will this help exactly?