There is no useful purpose in this politically driven policy other than harvesting votes from low-information voters.  Armed citizens carry firearms in and out of government offices now on a daily basis, and they are NOT the problem.  What will be the problem, is a wanna-be jihadist looking for a soft target.  A government office would be a handsome target - especially if it is an easy target (unarmed).  There is also the ever-present possibility of an estranged husband / boyfriend showing up at the office to kill his wife / girlfriend.  This is the most common  'workplace violence' scenario, second only to armed robbery of retail operations (convenience stores, delivery drivers, etc.).   This policy is nothing more than a solution in search of a problem.