A SOFA you suggest would take months to negotiate. If we are going to occupy the border towns we should just do it. It is easy. I personally witnessed US Army MPs patrolling with the “empty holster” PDF in Panama.
I agree with most of what you said, but A SOFA Agreement is not what I envisioned. A simple temporary agreement to join forces on Mexican soil until the threat is eliminated could be accomplished between the two Presidents as a national Emergency affecting both Nations.