The term “designated survivor” is used in a variety of ways, but in American politics, it refers to a member of the presidential line of succession who remains in a secure and distant spot when the other members of the line of succession are gathered in the same location. Designated survivors are used during the State of the Union Address, presidential inaugurations and other events where all of the people in the presidential line of succession might be reasonably expected to gather. The idea behind having a designated survivor is that in the event of a catastrophic event, at least one person would be around to take on the mantle of the presidency. Members of the presidential line of succession generally take turns acting as the designated survivor.
This concept evolved during the Cold War, when the United States government was concerned about the possibility of a nuclear attack that could wipe out all of the elected officials at a major event or meeting. There are situations when the president, vice president, speaker of the House, president pro tempore of the Senate and members of the Cabinet might be gathered together. These situations could present a significant security vulnerability, and the designated survivor concept is designed to reduce that vulnerability.
The identity of the designated survivor is often kept confidential until the last minute. The location where he or she is sheltered is always kept confidential. Along with a designated survivor to take over the presidency, the U.S. government also usually shelters a high-ranking senator who could take over as president pro tempore and a representative who could step in as the speaker of the House.
A catastrophic event that would require the services of designated survivors had yet to occur by the early 21st century. Many legal issues could arise if most of the people in the presidential line of succession were to be wiped out, especially if Congress was affected as well. For example, while appointing a designated survivor to take over as the speaker of the House might sound logical, the speaker is an elected official, and the House of Representatives would need to be able to form a quorum to elect the designated survivor for him or her to be legally empowered. The same is true of the president pro tempore of the Senate, who also is an elected member of the government.