Gun free military bases and recruitment centers date back to Clinton. Bush II continued the policy even after 9-11!

"A Clinton Administration revision to Department of Defense Directive 5210.56 — Army Regulation 190-14, dated 12 March 1993 — permits the Secretary of the Army to authorize military personnel to carry firearms “on a case by case basis” for personal protection within the continental United States, but forbids military personnel to carry their own personal firearms and both requires “a credible and specific threat” before firearms be issued for military personnel to protect themselves. It further directs that firearms “not be issued indiscriminately for that purpose.”"
http://jneilschulman.rationalreview.com/...-hood-massacre/

Department of Defense Directive 5210.56 — Army Regulation 190-14, dated 12 March 1993
http://armypubs.army.mil/epubs/pdf/r190_14.pdf

Since the military is not allowed to defend itself:

Heroes should be protected': Senior GOP figures blame gun-ban in army recruitment centers for leaving Chattanooga victims unprotected as one vigilante begins his own armed guard in protest