Education Secretary Miguel Cardona was the designated survivor chosen to sit out Thursday's State of the Union, a White House official confirmed to CBS News. 

Who is the designated survivor for 2024?

Cardona is 16th in the presidential line of succession. He has served in the White House since the beginning of the Biden administration, having been approved by a vote of 64-33. 

What is a designated survivor?

Because the State of the Union is traditionally delivered in the House chamber before the vice president, a joint session of Congress and Cabinet members, all the members of the line of succession to the presidency are in attendance. In case of a catastrophic event targeting the chamber, one Cabinet member is selected by the White House to go to a secure location and sit out the speech and be ready to take over the presidency in case of such a disaster. 

The designated survivor is a Cabinet member who does not attend the State of the Union address and would take over the presidency in case a catastrophic incident at the Capitol causes the death or incapacitation of everyone in the line of succession. This person is always chosen ahead of the State of the Union, and the White House refers to the individual as the "cabinet member not in attendance." 

The Presidential Succession Act of 1947 set the line of succession, which establishes who's next in line for the presidency if the office is vacated. Here are the first six in line: Vice President (Kamala Harris), Speaker of the House (Rep. Mike Johnson of Louisiana), Senate pro tempore (Sen. Patty Murray of Washington), Secretary of State (Antony Blinken), Secretary of Treasury (Janet Yellen), Defense Secretary (Lloyd Austin). 

How do they choose the designated survivor?

The designated survivor is usually chosen at random, according to the Constitution Center. Not all Cabinet members are eligible to be president — in the Biden administration, Energy Secretary Jennifer Granholm and Homeland Security Secretary Alejandro Mayorkas are both naturalized U.S. citizens and therefore not eligible to be president.

The person chosen to be the designated survivor is given some training ahead of time, although what exactly happens is classified. 

How is the designated survivor protected during the State of the Union?

The security around the designated survivor is mostly classified, although a few former designated survivors have described what they could about the experience.

Dan Glickman, who served as Secretary of Agriculture in the Clinton administration, wrote in Politico that he was "taken to a location outside of Washington (my daughter's apartment in New York), where I was accompanied by key military staff and Secret Service, including a military officer carrying what I presumed to be the nuclear football—a black, leather-encased aluminum briefcase that would be used to authenticate the person ordering a nuclear strike."

"It felt like an awesome responsibility to put on one man's shoulders, even if it was exceedingly unlikely the president—or in this case, the secretary of agriculture—would ever have to use it," Glickman wrote. "I sometimes wonder if I would have had the courage to give the order."

Who has been the designated survivor in the past?

It's unclear exactly when the tradition started, although generally it is considered to have originated during the Cold War. The first publicly announced designated survivor was in 1981, when the White House announced it would be Education Secretary Terrel Bell.

According to the Congressional Research Office, the designated survivor has most frequently been a secretary from the Departments of the Interior, Agriculture or Commerce. 

In the past 5 years, the designated survivor has been:

• 2023: Then-Labor Secretary Marty Walsh
• 2022: Commerce Secretary Gina Raimondo 
• 2021: No designated survivor was named since only 200 members of Congress attended amid the COVID-19 pandemic
• 2020: Interior Secretary David Bernhardt
• 2019: Energy Secretary Rick Perry 

In:
• State of the Union Address

Caroline Linton is a senior editor on the political team for CBSNews.com. She has previously written for The Daily Beast, Newsweek and amNewYork. She is currently based out of Austin, Texas, and writes and edits about local, state and national politics.