I was listening to the radio and learned about the term: designated survivor.
A clearly defined line of succession has been established for when the U.S. president is … unavailable. And if everyone in that line of succession is likewise … unavailable … then a person is arranged to be the designated successor. For example, during the State of the Union Address, pretty much everyone in the presidential line of succession is in attendance. If something were to happen to everyone attending that event, then the designated survivor would become Acting President.
During the event, the designated survivor is given presidential-level security and waits out the time at an undisclosed location.
So that’s a thing I learned today on the drive home from the gym.