When leaders of the United States all get together in one location, one of them is always absent.
That person is called the "designated survivor," and is tasked with leading the country on an interim basis should something terrible happen that incapacitates all governmental leaders who outrank him or her. On Tuesday night, many of them will gather on Capitol Hill to watch U.S. President Barack Obama's State of the Union Address at 9 p.m. ET. But the designated survivor will stay away.
This year's designated survivor is...
Transportation Secretary Anthony Foxx. So he'll be at an undisclosed location during Tuesday night's speech.
Foxx became transportation secretary in 2013. As such, he is the 13th in the line of succession for the presidency.
Before serving in the Cabinet, Foxx was the mayor of Charlotte, North Carolina, from 2009 to 2013.
Why does the U.S. need a designated survivor?
The State of the Union is like a school assembly. It's the only time every year that federal officials from all areas -- members of U.S. Congress, Supreme Court justices, presidential cabinet members -- gather in one room to listen to the president outline his agenda. Someone has to lead the country if something incapacitates the majority of the government's higher-ups.
When did this start?
The tradition may have started in the 1960s during the Cold War, when the U.S. was under a looming threat of nuclear assault. That said, a record of designated survivors' names only dates back to 1984.
How is the designated survivor chosen?
The White House chief of staff picks a member of the president's cabinet to be the designated survivor.
Where does the designated survivor stay? And how is she or he kept safe?
The designated survivor stays at an undisclosed location every year, and since the attacks of Sept. 11, 2001, he or she enjoys a security team fit for the president.
Before 9/11, the chosen survivor had to be away from colleagues, but security back then was not as big of a concern. One survivor, former Health and Human Services secretary Donna Shalala, ate pizza at the White House during the 1996 State of the Union, although survivors are usually out of town.
Survivors also get their own military assistant, who carries a briefcase full of the nation's nuclear launch codes, for the event.
Who has the designated survivor been in the past?
Usually, the position is given to a low-ranking cabinet member. The secretary of the interior and secretary of agriculture have been common choices in the past, but White House Chief of Staff Denis McDonough has chosen the secretary of energy twice in the past two years. Last year's choice was Secretary of Energy Ernest Moniz.
Former Secretary of Agriculture Dan Glickman described his curious experience as 1997's designated survivor to CBS News in 2007. Glickman said that when he decided to visit his daughter in New York City, he was flown in with a government aircraft, and driven to her door in a presidential motorcade.
Glickman added that a member of his security detail held the “nuclear football," which is the 45-pound briefcase containing the nuclear launch codes.