President Donald Trump signs his first executive order in the Oval Office of the White House, Jan. 20, 2017, in Washington.
AP Photo / Evan Vucci
President Lyndon Johnson signs the Civil Rights Act in the East Room of the White House in Washington, July 2, 1964.
Former President Ronald Reagan doffs his baseball cap, exposing his partially shaved head before the applause of well wishers who saw him off at the airport in Rochester, Minn., Sept. 15, 1989, one week after he underwent skull surgery at the Mayo Clinic. His wife Nancy puts her hand over his head from behind.
AP Photo / Jim Mone
President George Bush, left, walks with former Presidents Ronald Reagan, Jimmy Carter, Gerald Ford and Richard Nixon in the courtyard of the Ronald Reagan Presidential Library Simi Valley, Calif., Nov. 4, 1991.
AP Photo / Marcy Nighswander
President Richard Nixon stands on the bumper of his car as he reaches to shake hands in downtown Mobile, Ala., on May 25, 1971. Nixon was in Alabama to mark the start of the construction on the Tennessee-Tombigbee Waterway.
AP Photo / Chick Harrity
President George W. Bush hosts President-elect Barack Obama, and former presidents, from left, George H.W. Bush, Bill Clinton and Jimmy Carter, Jan. 7, 2009, in the Oval Office of the White House in Washington.