What would it take for the US president to leave Washington DC though? Obviously a real possibility of nuclear war. What else though?
Also President Madison evacuated Washington, DC during the War of 1812.
Where would he go? Australia ?
There's the Pentagon, Raven Rock Mountain Complex, Mount Weather Emergency Operations Center, Cheyenne Mountain Complex, the Greenbrier bunker, the Peters Mountain facility, 33 Thomas Street, nearly a dozen aircraft carriers, Camp David, and god knows how many military bases.
Or he could just board the doomsday fleet of E-4Bs and stay in the air
Government Continuity of Operations:
Continuity of Operations (COOP) is a United States federal government initiative, required by U.S. Presidential Policy Directive 40 (PPD-40), to ensure that agencies are able to continue performance of essential functions under a broad range of circumstances. PPD-40 specifies certain requirements for continuity plan development, including the requirement that all federal executive branch departments and agencies develop an integrated, overlapping continuity capability, that supports the eight National Essential Functions (NEFs) described in the document.
<https://en.wikipedia.org/wiki/United_States_federal_governme...>
See also:
Post Attack Command and Control System: <https://en.wikipedia.org/wiki/Post_Attack_Command_and_Contro...>
United States Continuity of Operations Facilities: <https://en.wikipedia.org/wiki/United_States_Continuity_of_Op...>
Nowhere. AF1 can be refueled in the air indefinitely, and carries enough food and water for several days. You ground civilian traffic and shoot down anything non-military in the air; nothing's getting to you.