Designated survivor

The designated survivor (also called designated successor) is a member of the US president's cabinet who goes to a remote, secure location at a time when all the government leadership is gathered in one place, such as during the State of the Union speech or a presidential inauguration. This is to make sure that the government will continue in case of some catastrophe that would result in harm to the President and many top elected officials at once.
The recent designated survivor is Sonny Perdue, President Donald Trump's Secretary of Agriculture, for the 2018 State of the Union Address.