25 Moments of the First 100 (25 images)

President Barack Obama enters the the Oval Office to begin his first day as President of the United States, at the White House in Washington on January 21, 2009. (UPI Photo/Pete Souza/White House)

U.S. President Barack Obama meets with White House Chief of Staff Rahm Emanuel in the Oval Office at the White House on his first full day in office in Washington on January 21, 2009. (UPI Photo/Pete Souza/White House Press Office)

U.S. President Barack Obama (C) is applauded by Vice President Joseph Biden (L) and a group of retired military officers after he signed executive orders to close the Guantanamo Bay Detention facility, on his desk in the Oval Office at the White House in Washington January 22, 2009. (UPI Photo/Matthew Cavanugh/Pool)

Chief Justice John G. Roberts Jr. administers the oath of office a second time in the Map Room of the White House on January 21, 2009. In what White House counsel Greg Craig called "an abundance of caution," a inauguration day mistake in word order was corrected. (UPI Photo/Pete Souza/The White House)