US Vice President Dick Cheney will asume the powers of the presidency tommorrow, when the current President undergose a routine colonoscopy.

Cheney will assume the powers, under section 3 of the 25th Amendmant, which permits through written decleration to the president pro-tempore of the senate, and speaker of the US house of Representatives that the president is unable to discharge his duties (this time because of the anesthesia) and the VP will become Acting President.

The 25th Amendment has been used many times in the past, because of its implications on the executive branch. the Amendment aloows for the replacement of a vice president (used twice in the 1970's, the first for the Appointment of Vice President Gerald Ford in 1973, the second for the Appointment of Vice President Nelson Rockefeller in 1974), the succession of Vice President to President (Succession of President Gerald Ford, after Nixon's resignation, 1974)

the 25th Amendment also allows for the order of succession to take place, so that there is always a president of America, a proceess which has meant since 9/11 a member of the executive branch(a member of the cabinet) as well as one member of congress and a senator are absent from major political events, such as the State of the Union.
The current order is as follows;

1 Vice President of the United States and President of the Senate Dick Cheney
2 Speaker of the House of Representatives Nancy Pelosi (Democrat)
3 President of the Senate pro tempore Robert Byrd (Democrat)
4 Secretary of State Condoleezza Rice
5 Secretary of the Treasury Henry Paulson
6 Secretary of Defense Robert Gates
7 Attorney General Alberto Gonzales
8 Secretary of the Interior Dirk Kempthorne
9 Secretary of Agriculture Mike Johanns
-- Secretary of Commerce Carlos Gutierrez
(ineligible; not a natural-born citizen)†
-- Secretary of Labor Elaine Chao
(ineligible; not a natural-born citizen)†
10 Secretary of Health and Human Services Michael Leavitt
11 Secretary of Housing and Urban Development Alphonso Jackson
12 Secretary of Transportation Mary Peters
13 Secretary of Energy Samuel Bodman
14 Secretary of Education Margaret Spellings
15 Secretary of Veterans Affairs Jim Nicholson
16 Secretary of Homeland Security Michael Chertoff ††

The 25th Amendment, which is used form time to time in reality is used incredibly frequently in Fiction, especially 24(see the 2nd, 4th and 6th days for its uses) Not surprisingly it is also used in political shows Commander in Chief, and The West Wing (where in both shows a vice presidents were appointed under the amendment). its also a major, sub plot to the movie Air Force One, where the cabinet try to pursdae the Vice President (played by Glenn Close) to assume the powers under section 4 of the amendment (again see 24; days 2, 4 and 6 for its fictional use). And in Tom Clancy's book 'Executive Orders' the start of the book sees the President and the majority of cabinet, and congress killed in a terrorits attack on congress.