Any Mayor worth their salt will have armed guards (police/security) at these shopping centers with recruitment offices. If the military says anything, they can be reminded that there are other business at those centers and they have a right to be protected. The Mayor can say, “We want the recruitment office to be there, but we know if the recruitment office is attacked by Islamic Terrorist Radicals... At least the other businesses will have protection.”
That sounds like a good plan, but we know none of the cities with liberal mayors are going to provide protection.
I’m surprised Washington hasn’t tried to say those offices are Federal territory and demand ban or arrest of anyone standing outside trying to protect them.
Set up recruting stations at gun shops with a shooting range in the back.