Although the Constitution clearly prohibits any religious requirement for public office, almost every single president has been a believer.
There has never been a self-identified atheist at the highest elected U.S. office, but views and denominations have varied -- though the vast majority have been Protestants, according to the Pew Research Center.
President Trump joins eight other presidents who grow up in the Presbyterian Church. He has called it a "wonderful religion." The first Presbyterian president was Andrew Jackson and the last one before Trump, Ronald Reagan.
President Trump takes the oath of office as first lady Melania Trump holds the Bible with his son, Barron. (Photo by Chip Somodevilla/Getty Images)
Presbyterian: Andrew Jackson (7), James K. Polk (11), James Buchanan (15), Gover Cleveland (22,24), Benjamin Harrison (23), Woodrow Wilson (28), Dwight D. Eisenhower (34), Ronald Reagan (40), and Donald J. Trump (45)
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About a quarter of the presidents -- including George Washington, James Madison, Franklin Roosevelt and the late George H.W. Bush -- were members of the Episcopal Church, the American successor to the Church of England.
In this Jan. 20, 1989 photo, President George H.W. Bush raises his right hand as he is sworn into office as the 41st president of the United States by Chief Justice William Rehnquist as first lady Barbara Bush holds the Bible for her husband. (AP Photo/Bob Daugherty, File)
Episcopalian: George Washington (1), James Madison (4), James Monroe (5), William Henry Harrison (9), John Tyler (10), Zachary Taylor (12), Franklin Pierce (14), Chester A. Arthur (21), Franklin D. Roosevelt (32), Gerald R. Ford (38), and George H.W. Bush (41)
Bill Clinton, Jimmy Carter, Harry Truman and James Harding are all Baptists, the next largest group with four, tied with Unitarians. John Adams, John Quincy Adams, William Taft and Millard Fillmore were all Unitarian.
President Bill Clinton waves as he visiting an U.S. American IFOR unit of the First Armoured Division in Hungarian town Taszar on January 13, 1996. PBEAHUMSEBO
Baptist: Warren G. Harding (29), Harry S. Truman (33), Jimmy Carter (39), and Bill Clinton (42)
Unitarian: John Adams (2), John Quincy Adams (6), Millard Fillmore (13), and Wiliam H. Taft (27)
George W. Bush is a Methodist, along with William McKinley and Ulysses Grant, while Barack Obama, Rutherford Hayes and Andrew Johnson are listed as non-denominational Christians.
Former President George W. Bush and other family members watch as the flag-draped casket of former President George H.W. Bush is carried by a joint services military honor guard to lie in state in the rotunda of the U.S. Capitol, Dec. 3, 2018. (AP Photo/Alex Brandon, Pool)
Methodist: Ulysses S. Grant (18), William McKinley (25) and George W. Bush (43)
Non-denominational Christian: Andrew Johnson (17), Rutherford B. Hayes (19) and Barack Obama (44)
Former US President Barack Obama gestures as he speaks during a town hall meeting at the 'European School For Management And Technology' (ESMT) in Berlin, Germany, Saturday, April 6, 2019. (AP Photo/Michael Sohn)
Other presidents in mainline Protestant denominations include Teddy Roosevelt and Martin Van Buren as Dutch Reformed and Lyndon Johnson and Andrew Garfield as Disciples of Christ. Herbert Hoover was the first Quaker and Richard Nixon was the last.
Dutch Reformed: Martin Van Buren (8) and Theodore Roosevelt (26)
Disciples of Christ: James Garfield (20) and Lyndon B. Johnson (36)
Quaker: Herbert Hoover (31) and Richard M. Nixon (37)
In this Jan. 20, 1961 file photo, President John F. Kennedy delivers his inaugural address after taking the oath of office on Capitol Hill in Washington. (AP Photo/File)
Calvin Coolidge is the lone Congregationalist and although Roman Catholicism is the largest denomination in the country, only one president, John F. Kennedy, was a Catholic.
Congregationalist: Calvin Coolidge (30)
Roman Catholic: John F. Kennedy (35)
The faith of Abraham Lincoln and Thomas Jefferson, both accused of being an atheist at one point in their lives, has been debated by scholars over the years. They are listed as having no formal affiliation, though Lincoln's Bible that surfaced last year offered more clues into his belief in God and reverence for the Bible. Jefferson, however, is a little more complicated, as he was known for not believing in Jesus' divinity, but believing in God.