But suppose they were able to purchase an actual nuclear DEVICE off the black market. A Soviet style suitcase nuke...not a dirty bomb. I think it changes the response dramatically.
They don't need soviet bombs, they're making them new from north korea and iran right now.
The devastation will be complete. 1 city, 20 trillion loss. If they threaten another, I hope you have a farm you can defend because our way of life is over.
Sure it does, but without the tritium, the Soviet style suitcase nuke will either be a purely fission detonation, or a very low order fission-fusion detonation.
In that situation, while we might feel entirely satisfied by responding with what they intended to use on us (thermonuclear, or 'fusion,' devices), the fact is, almost everything in our nuclear arsenal would far outclass what would have by then been suffered by us.
We have MOABs that, when deployed in clusters, can cause Hiroshima-scale destruction. That theoretical response is far better than some doctrine that locks us into obliteration of millions because of one nucdet on our soil.
The difference is not so obvious, I think. If these animals manage to detonate a nuclear device on US soil it will be a one time shot, given their palpably inferior skill for strategic thinking and industrial development in support thereof. MAD was devised as an entire repertoire of responses against another nation with ICBMs, SLBMs, intercontinental bombers, etc.