Actually, Obama's new nuclear policy doesn't change that much

And the Obama administration even gave itself an escape clause from that limited rule. “Given the catastrophic potential of biological weapons and the rapid pace of bio-technology development,” the new policy reads, “the United States reserves the right to make any adjustment in the assurance that may be warranted by the evolution and proliferation of the biological weapons threat.”

It’s a rather dense clause, but in explaining it, White House officials drew a distinction between non-nuclear threats that they view as only “crippling” and potential threats that might be “devastating.” They made clear that the administration reserves the right to determine which sorts of attacks might cross that line into “devastating,” and thus warrant a nuclear response.

So, is the entire declaratory doctrine a meaningless exercise in rhetoric? Not entirely. For one, it does weaken our deterrence ability slightly. Deterrence depends on an adversary fearing that we will respond in a devastating way to an attack. Policy makers like to think of our nuclear deterrence strategy as an “umbrella,” one that includes scenarios that the adversary is certain will engender our nuclear response, and others in which it believes that the chances of retaliation are too high to risk.