Why are there “designated survivors” during the State of the Union?

Virtually all the individuals who fall within the line of presidential succession customarily attend the State of the Union address. For this reason, protocols have been instituted to ensure continuity of government in the event of a catastrophe. Chief among these measures is the sequestration of a “designated survivor”—typically a member of the president’s cabinet—at a secure location away from the Capitol for the duration of the address. In the wake of the September 11 attacks, a similar system was enacted for the legislative branch, with two members of each house of Congress, one representing each party, absenting themselves from the address.