Is said government official housed in that building, as in does he or his organization rent office space there?
18 U.S. Code § 930 - Possession of firearms and dangerous weapons in Federal facilities
(a) Except as provided in subsection (d), whoever knowingly possesses or causes to be present a firearm or other dangerous weapon in a Federal facility (other than a Federal court facility), or attempts to do so, shall be fined under this title or imprisoned not more than 1 year, or both.
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(g) As used in this section:
(1) The term “Federal facility” means a building or part thereof owned or leased by the Federal Government, where Federal employees are regularly present for the purpose of performing their official duties.