Just for kicks, I decided to compile a list of men who were “a heartbeat away from the Presidency” owing to a vacancy in the Vice Presidential office (through death or resignation of the VP or his succession to the Presidency). It turns out there was quite a lot of time during which people not elected (except by their state or congressional district) were first in line for the Oval Office. Some are relative nonentities, some famous at least in a historical context. It includes a scad of Presidents Pro Tem (before 1886), seven Secretaries of State, four Speakers of the House, and one Secretary of the Treasury (Morgenthau, during Truman’s first, VP-less term when Jimmy Byrnes was before the Senate for confirmation as Secretary of State).
April 20, 1812- March 4, 1813 – William H. Crawford
November 25, 1814-March 4, 1817 – John Gaillard
December 28, 1832-March 4, 1833 – Hugh Lawson White
April 4, 1841- May 31, 1831 – Samuel Southard
May 31, 1842 - March 4, 1845 – Willie Mangum
July 9, 1850 – December 20, 1852 – William R. King
December 20, 1852 – March 4, 1853 – David Rice Atchison
April 18, 1853-December 4, 1854 – David Rice Atchison
December 4, 1854 – Lewis Cass
December 5, 1854 - June 9, 1856 – Jesse D. Bright
June 9-10, 1856 – Charles E. Stuart
June 11, 1856 - January 6, 1857 – Jesse D. Bright
January 6, 1857-March 4, 1857 – James Mason
April 15, 1865-March 2, 1867 – Lafayette S. Foster
March 3, 1867- March 3, 1869 – Benjamin Wade
November 22, 1875-March 4, 1877 – Thomas W. Ferry
September 19, 1881-October 12, 1881 – Thomas F. Bayard
October 13, 1881-March 3, 1883 – David Davis
March 3, 1883-March 3, 1885 – George F. Edmunds
December 7, 1885-January 19, 1886 – John Sherman
January 19, 1886-March 4, 1889 – Thomas F. Bayard
November 21, 1899-March 4, 1901 – John M. Hay
September 14, 1901-March 4, 1905 – John M. Hay
October 30, 1912–March 3, 1913 – Philander Knox
August 2, 1923-March 4, 1925 – Charles Evans Hughes
April 12, 1945-June 27, 1945 – Edward Stettinius
June 27, 1945-July 3, 1945 – Henry Morgenthau
July 3, 1945-January 21, 1947 – James F. Byrnes
January 21, 1947-July 18, 1947 – George C. Marshall
July 18, 1947-January 3, 1949 – Joseph W. Martin
January 3-20, 1949 – Sam Rayburn
November 22, 1963-January 20, 1965 – John W. McCormick
October 10, 1973-December 6, 1973 – Carl Albert
August 9, 1974-December 19, 1974 – Carl Albert