Bruno Musconi/AP PhotoIn this Aug. 12, 1993, file photo, U.S. President Bill Clinton points out people in the crowd to Pope John Paul II as he arrives in Denver, Co.
Gabriel Bouys/AP PhotoPope Francis and President Barack Obama smile as they exchange gifts, at the Vatican Thursday, March 27, 2014. President Barack Obama called himself a "great admirer" of Pope Francis as he sat down at the Vatican Thursday with the pontiff he considers a kindred spirit on issues of economic inequality.
Filippo Monteforte/AP PhotoIn this June 13, 2008, file photo, Pope Benedict XVI and US President George W. Bush walk in the Vatican Gardens during their meeting at the Vatican.
Haraz N. Ghanbari/AP PhotoIn this July 10, 2009, file photo, President Barack Obama and first lady Michelle Obama meet with Pope Benedict XVI, Friday, at the Vatican.
Osservatore Romano/AP PhotoIn this June 4, 2004, file photo, President George W. Bush is greeted by Pope John Paul II upon their meeting in his private library at the Vatican.
Arturo Mari/AP PhotoIn this Sept. 10, 1987 file photo, Pope John Paul II, right, meets with President Ronald Reagan in the Vizcaya, a lavish mansion on Biscayne Bay, in Miami.
Paul Schutzer/AP PhotoIn this Dec. 6, 1959 file photo, President Dwight D. Eisenhower walks with Pope John XXIII at the Vatican.
AP File PhotoIn this Sept. 28, 1970, file photo, President Richard Nixon talks with Pope Paul VI as they meet in the Vatican.
AP File PhotoIn this Oct 6, 1979, file photo, President Jimmy Carter , right, talks with Pope John Paul II at the White House in Washington.
AP File PhotoIn this Oct. 4, 1965, photo, Pope Paul VI, left, and President Lyndon B. Johnson are seen during the Pontiff's visit to New York.
AP File PhotoIn this July 2, 1963 file photo, President John F. Kennedy and Pope Paul VI talk at the Vatican.
Ron Edmonds/AP PhotoIn this May 27, 1989, file photo, President George H. W. Bush gestures while standing with Pope John Paul II in the papal library at the Vatican.
Pablo Martinez Monsivais/AP PhotoUS President Barack Obama meets with Pope Francis, Thursday, March 27, 2014 at the Vatican. Obama called himself a "great admirer" of Pope Francis as he sat down at the Vatican Thursday with the pontiff he considers a kindred spirit on issues of economic inequality.
Gabriel Bouys/AP PhotoPope Francis meets President Barack Obama at the Vatican Thursday, March 27, 2014. President Barack Obama is holding a historic first meeting with Pope Francis, the pontiff that the president views as a kindred spirit on issues of economic inequality and the poor. Obama arrived at the Vatican Thursday morning amid the pomp and tradition of the Catholic Church, making his way to greet the pope after a long slow procession.