"In order to ensure continuity of government, Defense Secretary Robert Gates has been designated by the outgoing Administration, with the concurrence of the incoming Administration, to serve as the designated successor during Inauguration Day, Tuesday, January 20th," White House press Secretary Dana Perino said.
According to the Presidential Succession Act of 1947, if the president is unable to fulfill his duties, the Vice President succeeds him, followed by the Speaker of the House, the President pro tempore of the Senate (traditionally the senior member of the majority party), The Secretary of the Treasury, and then the Secretary of Defense. (The succession order continues from there – You can see the full list here.)
Perino said that Gates will be at a secure, undisclosed location on Inauguration Day, according to CBS News White House Correspondent Mark Knoller. Most of the others on the succession list, by contrast, will be participating in the inauguration festivities.
There is a long history of keeping designated individuals away from events at which numerous high ranking officials will be present. In 2007, for example, then-Attorney General Alberto Gonzales was kept away from the State Of The Union so that he could take over government in case of disaster.
At that time, Knoller spoke to Dan Glickman, who was the Cabinet member kept from the proceedings at President Bill Clinton's 1997 State Of The Union address. He was then the Secretary of Agriculture.
"I was not given a briefing on what to do if something happened," Glickman said. He did, however, have presidential-level security, for one night only.
"A government aircraft flew him to New York City – and a motorcade drove him to his daughter's apartment in lower Manhattan," Knoller wrote. "Not only did Glickman have a sizeable Secret Service detail, he says his entourage included a military aide that he thinks was carrying what's known as 'the football.' That's the special briefcase carrying the codes by which the President can launch nuclear missiles."