Best Case (POD: Dewey Defeats Truman):
33. Harry Truman (D): 1945-1949
34. Thomas Dewey (R): 1949-1957
35. Estes Kevaufer (D): 1957-1961
36. Henry Cabot Lodge (R): 1961-1969
37. Margaret Chase Smith (R): 1969-1973
38. Robert Kennedy (D): 1973-1981
39. George H. W. Bush (R): 1981-1989
40. Paul Simon (D): 1989-1997
41. Colin Powell (R): 1997-2005
42. John McCain (R): 2005-Present
Worst Case (POD: Wallace Renominated for Vice President in 1944. Yes, I am aware this is unlikely and nightmarish.):
33. Henry Wallace (D): 1945-1949
34. Robert Taft (R): 1949-1953 (Died in office, 1953)
35. Joseph McCarthy (R): 1953-1957
36. Richard Russell (D): 1957-1965 [For those (like me) who don't know who he is without using Google, he was a leading segregationist who represented Georgia in the Senate.]
37. George Wallace (D): 1965-1968 (Assassinated 1968)
38. James Eastland (D): 1968-1973 [The Progressive Party, led by George McGovern, emerges in 1972.]
39. Phyllis Schlafly (R): 1973-1981 [Election of 1976, between Schlafly, Democrat Robert Byrd, and Progressive Robert Kennedy, is decided by the House of Representatives.]
40. John Rarick (D): 1981-1985 [OTL Congressman and American Independent Party Presidential Nominee in 1980. Escalates the Cold War and pushes to ban the Progressive Party for alleged "Soviet sympathy." Assassinated by a Socialist in 1985.]
41. Jesse Helms (D): 1985-1989 [Attempts to break up the Progressive Party using the National Guard in the aftermath of Rarick's assassination. American people finally reject the Democratic Party in 1988.]
42. Noam Chomsky (P): 1989-1995 [Elected as an avowed Socialist. Assassinated in 1995.]
43. Jesse Jackson (P): 1995-2001
44. Elizabeth Dole (R): 2001-2005 [Moderate, but generally incompetent.]
45. Hillary Rodham (P): 2005-Present