Page "Designated survivor" Paragraph 2

Since 2005, members of Congress have also served as designated survivors.

In addition to serving as a rump legislature in the event that all of their colleagues were killed, a surviving Representative and Senator could ascend to the offices of Speaker of the House and President Pro Tempore of the Senate, offices which immediately follow the Vice President in the line of succession.

If such a legislative survivor were the sitting Speaker or President Pro Tempore – as for the 2005, 2006, and 2007 State of the Union addresses, in which President Pro Tempore Ted Stevens ( R-Alaska ) or Sen. Robert Byrd ( D-West Virginia ) was also a designated survivor – he or she would become the acting president rather than the surviving Cabinet member.

However it is unclear whether another legislator could do so without first being elected to that leadership position by a quorum of their respective house.