Ancient wisdom.
"If a man doesn't strike first, he will be struck first"
Athengoras of Syracuse
In certain situations, striking first is always the best ploy. Specifically, Iran.
Should we decide NOT to hit them (I find this incomprehensible at this point in time) we will be hit first.
Russia for the most part has proven they will not launch a nuclear strike first — UNLESS there is a good reason to do so, like cleaning up a situation that we’ve found ourselves.
China on the other hand, is well known to be planning to attack the United States in the future, whether by nuclear weapons or sea/air attacks, it’s not clear, but certainly the ability to defend ourselves against ICBMs is the best possible thing we can have at this time.