Others would be
John C Calhoun. Would have succeeded Had HoR failed to choose a President in 1825, or had Andrew Jackson succumbed to illness in 1829.
Willie Mangum. Would have succeeded had John Tyler been killed by the explosion on the
Princeton in 1844.
George M Dallas. Would have succeeded Polk had he died before leaving office, rather than three months
after doing so in 1849.
Lafayette S Foster. Would have succeeded Lincoln had assassin George Atzerodt not chickened out of killing Andrew Johnson in 1865.
Thomas W Ferry. Might have been interim President in 1877 had no result been declared for the 1876 election. Reportedly, Grant considered resigning in his favour (VP Henry Wilson had died in 1875) on March 3,so that he could serve pending a new election in Nov 1877.
Thomas F Bayard, David Davis, George F Edmunds. Presidents of Senate under Chester Arthur, who was in poor health and died the year after he left office. Any of them might have succeeded, depending exactly when he died. But see below.
Joseph Warren Keifer, John Griffin Carlisle. Speakers of House who would have succeeded had Arthur died while the Senate was in recess.
Adlai E Stevenson. Would have succeeded in 1893 had Cleveland succumbed to his operation for cancer.
Champ Clark. Received a majority vote at the 1912 Democratic convention, but lost out to Wilson due to an archaic rule requiring a two-thirds majority - the first candidate since Van Buren in 1844 to sufffer this fate.
Philander Knox. Would have been interim President had Taft died in late 1912, VP James S Sherman having died in October.
Charles Evans Hughes. Missed Presidency by a whisker in 1916, when only late returns from CA saved Wilson.
Irvine L Lenroot. Nominated for VP by supporters of Harding in 1920, but rejected by Convention in favour of Coolidge.
Alben W Barkley. Would have succeeded in 1950 had those Puerto Ricans succeeded in assassinating Truman.
