They have been shooting at us for years.
One time in El Paso, several years ago a group of agents was checking for sign on the river, when someone fired shots from Mexico. 8 agents returned fire!
One day when I was assigned an area that had our highest number of shootings and a dude on the south side was known to be shooting at agents with a high powered pellet rifle. I was checking my M-16 out of the arms room, when a supervisor happened by and asked "Why are you taking an M-16 to the headgates, it's only a pellet gun?" , I told him, "No, it was a pellet gun yesterday, today it may be a 308. Someone points a rifle at me and I am going to shoot them." He then went on about me creating an international incident, I told him, "No, I would be finishing an international incident."
The BP has been getting shot at for years, the BP gets in more shootouts than all of the other federal agencies combined. That factoid was from there were only about 4000 agents nationwide, now there are 20,000.