The only man (to date) to twice act as President of the United States, former Vice President Richard Bruce "Dick" Cheney.

Slightly over five years following his initial invocation of the 25th Amendment, on July 20, 2007, President George Walker Bush's medical team advised the media that the President would once again undergo a colonoscopy procedure, during which time Vice President Richard Bruce "Dick" Cheney would temporarily act as President of the United States.  As in 2002, Bush opted to invoke Section 3 of the 25th Amendment, and at 7:16 a.m. on July 21, 2007 he signed a letter to that effect, having it transmitted by facsimile to House Speaker Nancy Pelosi, Senate President Pro Tempore Robert C. Byrd, and Vice President Cheney as well:

Text of Letter Transmitted at 7:16 a.m.

Dear Mr. Speaker (Dear Mr. President):

As my staff has previously communicated to you, I will undergo this morning a routine medical procedure requiring sedation.  In view of the present circumstances, I have determined to transfer temporarily my Constitutional powers and duties to the Vice President during the brief period of the procedure and recovery.

Accordingly, in accordance with the provisions of Section 3 of the Twenty-Fifth Amendment to the United States Constitution, this letter shall constitute my written declaration that I am unable to discharge the Constitutional powers and duties of the office of President of the United States.  Pursuant to Section 3, the Vice President shall discharge those powers and duties as Acting President until I transmit to you a written declaration that I am able to resume the discharge of those powers and duties.

George W. Bush

What Happened Next

Acting President Cheney served for two hours and five minutes in this instance, and unlike the previous two times the nation had an Acting President, Cheney was documented as actually doing something outside his normal routine.  Aware of the fleeting, footnote-like historical situation he was in, Acting President Cheney took at least a portion of his time as our temporary Commander-in-Chief to write a letter to his grandchildren.  Typical of the public perception of Cheney, it wasn't exactly bursting with warm, loving sentiments:

Dear Katie, Elizabeth, Grace, Philip, Richard and Sam,

As I write this, our nation is engaged in a war with terrorists of global reach.  My principal focus as Vice President has been to help protect the American people and our way of life.  The vigilance, diligence and unwavering commitment of those who protect our Nation has kept us safe from terrorist attacks of the kind we faced on September 11, 2001.  We owe a special debt of gratitude to the members of our armed forces, intelligence agencies, law enforcement agencies and others who serve and sacrifice to keep us safe and free.

As you grow, you will come to understand the sacrifices that each generation makes to preserve freedom and democracy for future generations, and you will assume the important responsibilities of citizens in our society.  I ask of you as my grandchildren what I asked of my daughters, that you always strive in your lives to do what is right.

May God bless and protect you,
Richard B. Cheney
Acting President of the United States
(Grandpa Cheney)

Letter Transmitted at 9:21 a.m.

Dear Madam Speaker (Dear Mr. President):

This letter shall constitute my written declaration that I am presently able to resume the discharge of the Constitutional powers and duties of the office of the President of the United States.

George W. Bush