The issue is, our nuclear force has decayed. We need a more credible first strike capability. Russia bolsters it nuclear force.

I used to buy into MAD, but thought experiments in light of recent events have changed my mind.

Suppose Russia rolls into Estonia. With a weak nuclear arsenal and conventional force (which, thankfully, we don't have), sufficient only to devastate Russian cities but with no counterforce capabilities, we can:

1. Use our nuclear weapons and bear the full Russian response (commit suicide but do significant damage to Russia)
2. Let them have it.

With a credible first strike capability and a large conventional force, we can escalate conventionally to test Russian resolve. The question becomes the resolve of Russia and limits the requisite resolve on the part of the United States.