I believe that this war has already begun. With armed gangs like the one you mentioned, our military can be engaged with the training that they go through. This is what our military is about: Breaking things and killing people. These fit that bill perfectly.
I'm doing my best to figure out where you are coming from.
Obviously - you don't think the military should be put on the US border. I disagree.
However - I don't think that the U.S. Military should be put on the U.S. Border to act as police and arrest people.
I think the U.S. Military should be put on the border to protect the country by killing and destroying the invaders.
Let the existing border patrol handle the legal entry points into the U.S. - but put the military everywhere else. And order them to protect the border at all costs.
I'm not talking about just a couple military patrols with humvees and .50 cal... I talking about a full scale operation with air support and a free fire zone - anything and anyone seen crossing into the U.S. should be destroyed immediately - no questions asked.
I sincerely believe that after a few days of death - the invasion would stop.