My main fear is that the Mexican Army will start patroling or escorting illegals into our country rather than protecting drug runners.
What will be the fallout from a firefight involving US citizens and a foreign military on our side of border? A liberal media white wash (yep!), or the Bush Administration finally mobilizing (iffy - at best!) to help our citizenry and stop illegals at the border?
Well, last time, when Mexican police/troops on their side of the border shot and killed a U.S. federal officer, they just covered it up and claimed it didn't happen that way. I wonder if the shooters got the promised $200,000 bounty for killing an American federale.
Bush hasn't even met with the family of the murdered officer, the coward. Too busy counting his share of the money he gets from PEMEX, I guess.
Something along those lines has happened before. Take a look at this story. Granted it happened some time ago.
Here is another that happened more recently involving Border Patrol agents and Mexican 'citizens'. Sort of the reverse of what you suggested but it still goes to the issue of cross border firefighting incidents.