So in my world, the entire White House area has been turned into a small fortress/FOB. Due to the post-apocalyptic dystopian state of my world what with zombies, breakaway secessionist states, hostile militias, bandits, etc. roving around in the ruins of modern civilization after the Great Collapse (2006-2010), the White House has been converted into a small fortress manned by a joint Secret Service-US Garrison (essentially the US military consolidated into a single branch) detachment numbering in at over 500 Troopers and Secret Service agents. The President of the United States still lives and works in the White House (and no, the remnants of the United States aren’t a dictatorship, elections still happen) along with the First Family and civilian federal employees are also working in there too.
And yes I know that the White Houde already has a crazy stupid amount of security already but I was thinking of adding watch towers, gates, one or two helipads, barbed wire, machine gun nests, defensive barriers like HESCO blocks, etc.
But in an emergency scenario, how effective would the White House serve as a base of operations/FOB? Can it actually work or no?