WASHINGTON (AP) — Just minutes after George W. Bush took the oath of office eight years ago, he signed papers formally nominating 13 Cabinet-level officials. Several hours later, the Senate, meeting in a special Saturday session, confirmed seven Cabinet secretaries, including the heads of the key posts at State, Treasury and Defense.

That swift and seamless transition, expected to be repeated when Barack Obama is sworn in as president on Jan. 20, reflects a long tradition of the Senate giving deference to a new president’s picks for his leadership team. Also in play is the post-Sept. 11 resolve that there be no interruption in the line of succession if the president or other leaders die or are disabled.

Obama moved quickly to choose core members of his Cabinet, including Sen. Hillary Rodham Clinton to head the State Department, New York Federal Reserve Bank president Timothy Geithner to be treasury secretary and Robert Gates to stay on as chief at the Pentagon.

Tradition calls for current Cabinet secretaries to prepare letters of resignation as the administration nears its end. But they all serve at the discretion of the president, and Bush has directed that they will formally leave office at noon on Jan. 20, concurrent to the swearing in of the new president.

The exception is Gates, who by becoming Obama’s defense secretary could move up in the line of presidential succession, although only for a few hours, if the Senate acts quickly to confirm Clinton or Geithner. Homeland Security Secretary Michael Chertoff also will keep his job briefly, until 9 a.m. on Jan. 21, to oversee the massive security operation for the inauguration.