Butterfly-lite, admittedly, but I could just make up all of the names and get to 50, so I'll keep it this way:
25. William McKinley (R), 1897-1901, assassinated on schedule.
26. Theodore Roosevelt (R), 1901-1905, dumped by conservative wing of party at convention.
(This is as close to a POD as you're going to get!)
27. Mark Hanna (R), 1905, survived sixteen more months than in OTL, died within a few months of taking office.
28. James Sherman (R), 1905-1909, took over after Hanna.
29. John A. Johnson (D), 1909, WJB doesn't run, Johnson beats Sherman in close election, but dies (as in OTL) September 1909.
30. George Turner (D), 1909-1913, Johnson's VP, took over for him, not renominated.
31. Woodrow Wilson (D), 1913-1916, resigned in November 1916 (as he threatened in OTL) after losing presidential election to
32. Charles Fairbanks (R), 1916-1918, died in office. Succeeded by his Vice-President
33. Theodore Roosevelt (R) 1918-1919, died in office. Succeeded by Secretary of State
34. Robert Bacon (R), 1919, died after two months in office, succeeded by Secretary of the Treasury
35. Andrew Mellon (R), 1919-1921, not renominated.
36. Warren Harding (R), 1921-1923, died in office. Succeeded by Vice-President
37. Asle Gronna (R), 1923, lives one year longer than in OTL, died in office. Succeeded by Secretary of State
38. Charles Evans Hughes (R), 1923-1929.
39. Guy D. Goff (R), 1929-1933, died in office two months before leaving office, succeeded by Vice-President
40. Hanford McNider (R), 1933. FDR gets assassinated by Zangara, so is replaced by VP-Elect
41. George Dern (D), 1933-1936 (Utah governor considered by FDR for VP in OTL). Dies in office, replaced by Secretary of State
42. Cordell Hull (D), 1936-1937.
43. William Borah (R) 1937-1940, died in office. Succeeded by Vice-President
44. William Knox (R) 1940-1944, died in office a few months earlier than OTL, succeeded by Vice-President
45. Charles McNary (R), 1944, died in office, succeeded by Secretary of State
46. John Foster Dulles (R), 1944-1945.
47. Cordell Hull (D), 1945-1948, resigned for medical reasons. Succeeded by Vice-President
48. James A. Roe (D), 1948-1950, assassinated by Puerto Rican nationalists, succeeded by Vice-President
49. Alben Barkley (D), 1950-1953, not nominated by party for 1952 election.
50. Estes Kefauver (D), 1953-
There you go, fiftieth president fifty-six years ago!
