Four Is Too Much
1941-1945: Franklin D. Roosevelt (D-NY)/Henry A. Wallace (D-IA)
1945-1953: Thomas E. Dewey (R-NY)/John W. Bricker (R-OH)
1953-1961: Dwight D. Eisenhower (D-NY)/Joe Kennedy Jr. (D-MA)
1961-1965: Joe Kennedy Jr. (D-MA)/Lyndon B. Johnson (D-TX)
1965-1977: Richard M. Nixon (R-CA)/Gerald Ford (R-NE)
1977-1985: Robert F. Kennedy (D-MA)/Jimmy Carter (D-GA)
1985-1989: Jimmy Carter (D-GA)/Mo Udall (D-AZ)
1989-1993: Pat Robertson (R-VA)/Phyllis Schlafly (R-MO)
1993-1997: Paul Tsongas (D-MA)/Jerry Brown (D-CA)
1997-2005: Jerry Brown (D-CA)/Al Gore (D-TN)
2005-2013: John McCain (R-AZ)/Dick Cheney (R-TN)
2013-present: Keith Ellison (D-MN)/Elizabeth Warren (D-MA)
Don't really want to get into specifics here, but basically, butterflies mean the war in Germany ends around July 1944, and the war in Japan ends between September and October. With that said, the American public doesn't want FDR as a peacetime president again, and they elect Dewey by a tight margin. Dewey isn't as politically savvy as Truman, so he compromises with the conservative coalition to save parts of the New Deal in exchange for gutting it in others. While this leads to short term prosperity, meaning Dewey defeats Stevenson in 1948, the economy recedes in the early 1950s and the conservatives lose their power over Congress. At the same time, the Democrats successfully elect Eisenhower, and he beats Bricker in 1952 and 1956. Since Joe Jr. lives through the war, he acts as Eisenhower's VP and is elected in his own right against Nelson Rockefeller in 1960, but a combination of voter fatigue and a generally uninspiring presidency gives Nixon the White House in 1964. Due to the lack of a 22nd Amendment, Nixon beats LBJ in 1968 and Humphrey in 1972, but years of scandals catch up with him, and alongside a worsening economy, he is forced out in 1976. RFK doesn't run in 1968, so by 1976 he's built up a significant enough coalition that he takes the nomination and the presidency against Ford. He beats Reagan in 1980, and Carter holds off Baker in 1984, but 12 years of socially liberal presidencies radicalises the Moral Majority by 1988, and they rally around Robertson. Now, Pat Robertson's presidency is a fucking disaster, and he pisses off most everybody outside his party to the point that he loses in a landslide to Tsongas in 1992, discrediting the Moral Majority entirely. Cancer means Tsongas doesn't seek another term in 1996, so his VP wins resoundingly against someone like, idk, Ron Paul. Brown beats GWB in 2000, but due to 9/11 or some equivalent attack, neocons sharply criticise Brown's foreign policies and national security commitments. John McCain beats Gore in 2004, staves off the recession by a year, beats Obama in 2008 despite starting a war in Iraq, and pisses off everyone when the recession comes about and he bails out the rich. After a heated primary, Keith Ellison wins in 2012, and despite the growing threat of the far-right, his presidency has been so successful that he's running for a third term this year.