I stopped reading this thread because it fails miserably.
This is a Presidential appointment position. It is custom for appointees to offer their resignation letters to the incoming President. Trump accepted this one (and countless others) so it therefore goes into effect at noon on inauguration day. No politics and no subterfuge - it just works out that way. It should have no effect on the security plans. They are not plotting the Battle of the Bulge here.... just a simple security plan and the units have commanders who understand the plan. It is crowd control - not combat.
I would expect a journalistic frenzy over this because they do not understand it, but all the angst on this thread is disappointing.
A person close to the Trump transition team reportedly said transition officials wanted to keep him, but the Army pushed for a replacement. Schwartz