Even that doesn't help. There are a zillion possible beneficiaries to any major attack, and some attackers do it for the lulz with no benefit at all. If you can't reliably identify where an attack originated then deterrents are meaningless.
I forget where (Terminator 2?) but there was definitely an SF story somewhere where the aggressor launched a nuclear attack at their victim's enemy rather than straight back at the victim they'd gained control of, because the likely counterattack was more powerful than the first strike.
I don't know to what extent military personnel these days actually have visibility of where the strategic weapons they control are targetted but I suspect that they might refuse to launch on targets in their own country.
The scenario is from the Terminator series.. I always thought it was simpler to just press "LAUNCH" than to reconfigure all the targets. From the perspective of Skynet, the Russian response would be faster than relocating all the missiles in the US, then launching, so that's the course of action.
