Following on to this question... since a military aide is always near the President with the Football, how does the new President get the football if that aide with the football is with the now-former President over -- for example -- the South Pacific in formerly-Air Force One?
Would these aides somehow conspire to not be in the plane with the President? Or would "they" tell the President that the Football is staying in Washington?
There are three nuclear footballs in total. Two are allocated to the president and vice president, with the last being stored in the White House. In Presidential transitions, the president-elect does not receive the actual nuclear code card until after the nuclear briefing, when "he meets with the outgoing president at the White House just before the actual inauguration ceremony. The code card is activated electronically right after the president-elect takes the oath at noon". -Wikipedia
With outgoing President Donald Trump skipping president-elect Joe Biden's inauguration ceremony to instead spend the afternoon in Florida, a literal handoff of the nuclear codes is not possible.
Instead [...] the U.S. military has designed a "more complicated" handover involving two separate black bags. "At noon, the set of codes that Donald Trump has will become inactive – and at that moment, the set of codes that Joseph Biden has will become active." - Article