One of the more mysterious aspects of the annual State of the Union address is the role of the designated survivor, which in 2023 will be Labor Secretary Marty Walsh.

Each year, someone in the presidential line of succession is chosen not to attend the speech inside the Capitol building in case of a catastrophic event.

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Walsh, who is reportedly leaving his post to work for the NHLPA, holds that distinction this year.

Last year's designated survivor was Commerce Secretary Gina Raimondo, who watched the speech in a remote location far from the Capitol dome.

The designated survivor tradition dates to the 1950s and the Cold War. Members of the president's Cabinet are in the line of succession following the vice president, speaker of the House, and president pro tempore of the Senate. In addition to the State of the Union address, designated survivors have been named for presidential inaugurations and joint sessions of Congress.

Congress itself also designates members of the House and Senate from each party to play a designated survivor role in order to keep the legislature alive in the case of a catastrophic event.

Though relatively obscure, the practice gave name to the show Designated Survivor, which ran for three seasons on ABC and Netflix beginning in 2016 and depicts a fictional secretary of housing and urban development who ascends to the presidency following an explosion.

Some prominent previous designated survivors have included former Gov. Andrew Cuomo (D-NY), former Secretary of State Hillary Clinton, former Agriculture Secretary Tom Vilsack, former Sen. Orrin Hatch (R-UT), and former Gov. Rick Perry (R-TX).

Like Clinton and Vilsack, Cuomo and Perry were designated survivors in their capacities as Cabinet officers. Hatch was president pro tempore of the Senate.

In President George W. Bush's speech to Congress after the 9/11 terrorist attacks in 2001, Vice President Dick Cheney was the designated survivor.

When most of the Cabinet watched President Joe Biden's first address to a joint session of Congress remotely in 2021, there was no specific designated survivor. Treasury Secretary Janet Yellen was the Cabinet officer highest up in the line of presidential succession who was not present.

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Here is a full list of recent State of the Union designated survivors.

2010: Secretary of State Hillary Clinton and Housing and Urban Development Secretary Shaun Donovan

2011: Interior Secretary Ken Salazar

2012: Agriculture Secretary Tom Vilsack

2013: Energy Secretary Steven Chu

2014: Energy Secretary Ernest Moniz

2015: Transportation Secretary Anthony Foxx

2016: President Pro Tempore Orrin Hatch and Homeland Security Secretary Jeh Johnson

2017: Veterans Affairs Secretary David Shulkin (joint session of Congress)

2018: Agriculture Secretary Sonny Perdue

2019: Energy Secretary Rick Perry

2020: Interior Secretary David Bernhardt

2021: Treasury Secretary Janet Yellen (unofficially due to remote address)

2022: Commerce Secretary Gina Raimondo