I would nuke Mexico.
Simply because Cuba & Venezuela r anti-U.S.A...by being closer to Fidel Castro & Hugo Chavez. The communication & military supplying would be alot easier, also it will surely be able to convince all of S.America to join in on invadeing the U.S.A...
Mexico would be right in U.S.A's backyard...Cuba & Venezuela r than welcome to land all of their military might right in Mexico & unite.
Start a battlefront on the borders of California state & up to Washington state, cut off the pacific ocean water supplies.
The other would be to move into Texas & eastward conquering Louisiana, Florida etc cutting off the Gulf...
Landlock all of the west & central states from water supply, cut off all river flow from the oceans that lead to innerland.
Yep Mexico would be the ideal strategic point of interest.