Thus far, fifteen U.S. Presidents have also served in the U.S. Senate: James Monroe, John Quincy Adams, Andrew Jackson, Martin Van Buren, William Henry Harrison, John Tyler, Franklin Pierce, James Buchanan, Andrew Johnson, Benjamin Harrison, Warren G. Harding, Harry S. Truman, John F. Kennedy, Lyndon B. Johnson and Richard M. Nixon.

That number will increase by one on January 20, 2009, with the inauguration of the 44th President of the United States.