the possible costs. In a nuclear exchange, even the winner would be severely punished. A small deterrent force is sufficient, since an attacker can never be certain of destroying all of the defender's nuclear weapons.
The danger of "irrationality" may be exaggerated. In the past, even "irrational" Third World rulers, notably Uganda's Amin or Libya's Muammar al-Qaddafi, have backed down when faced with the threat of superior conventional enemy force; there is no reason to think...