1968: Humphrey def. Reagan
1972: Humphrey (inc.) def. Rockefeller
1976: Buckley def. Muskie (inc.)
1980: Church def. Buckley (inc.)
1984: Bayh (inc.) def. Bush
1988: Bayh (inc.) def. Dole
1992: Biden def. Janklow
1996: Kolbe def. Biden (inc.)
2000: Janklow def. Hunt (Pres. Kolbe defeated in primary)
2004: Jeb! def. Sanders
2008: Biden def. Jeb! (inc.)
2012: Wellstone def. Santorum
2016: Wellstone (inc.) def. Trump
2020: Cotton def. Klobuchar
2024: Pritzker, as of July 2022, leads the field to face Cotton (inc.)
Ignore that I went ham with the butterflies, okay?
Just for fun, same TL (but not same maps) with OTL candidates:
1968: Humphrey def. Reagan
1972: Humphrey def. Ashbrook
1976: Reagan def. Udall
1980: Carter def. Reagan
1984: Mondale def. Reagan
1988: Jackson def. Robertson
1992: Harkin def. Buchanan
1996: Specter def. Clinton
2000: McCain def. Bradley
2004: Bush def. Kerry
2008: Kucinich def. Giuliani
2012: Obama def. Santorum
2016: Sanders def. Trump
2020: Fellure def. Sanders