In the weeks following Sept. 11, 2001, experts repeatedly warned of an unnerving prospect: another terrorist strike against a prominent national symbol with some security measures in place, but far fewer safeguards than other targets. One icon long considered a potential target for would-be mass murderers: the Smithsonian Institution — with its millions of visitors and the national treasures its museums house.

But the Smithsonian acknowledged to The Washington Examiner that its guards do not routinely monitor the metal detectors installed at some of its most visited museums, allowing visitors to enter largely unscreened and potentially leaving the facilities vulnerable to attack using a smuggled, undetected weapon.