We have a finite number of weapons in the inventory. Every single one is assigned to a target. The evaluation criteria take into account military threat, political damage, economic damage, cultural and religious significance and population centers. It is a VERY thorough evaluation.
It was my personal policy to never peruse the weapons or targets lists while I worked on the project. I suspect both lists are in a constant state of re-evaluation.
re- nuke targetting. Let's hope none of the AQ lunatics studied trig or statistics.