[Matt Wiser]

This is '98: General Cummings and the JCS are the de facto government. CivGov hasn't yet been formed. The Joint Chiefs see a military situation on the southern border that cannot be solved via conventional means alone. Not to mention that SAC's remaining bombers by this time are likely dedicated nuclear strike platforms. The objective is threefold: blast Mexican supply lines to such a degree that effective restoration is almost impossible, force the invasion to a standstill, and to punish the Mexican Government for crossing the border in the first place. The latter is accomplished by a ALCM strike on the Presidential Palace on the "low" yield setting (20 KT). And with five weapons, six at the most, those objectives are accomplished. There's still Mexican forces north of the border, but now they're split into factions, and hopefully can be dealt with in the future.