Depends on how you look at it. As others have pointed out, Lyndon B. Johnson declined the nomination for Democratic Presidential candidate in March of 1968, we

Depends on how you look at it. As others have pointed out, Lyndon B. Johnson declined the nomination for Democratic Presidential candidate in March of 1968, well before both most of the primary contensts and the then-open Democratic Convention in Chicago. Rather famously, that convention didn't go particularly smoothly. (In an interesting coincidence, this year's Democratic primary is also in Chicago.) George McGovern's 1972 vice presidential nominee, Thomas Eagleton, stepped down after it was revealed Eagleton had undergone electroshock therapy, two weeks after the Democratic Convention. McGovern selected Sargent Shriver as the replacement candidate. Horace Greeley, Liberal Republican Party and Democratic Party candidate in the 1872 election, running against incumbent Ulysses S. Grant, died on 29 November 1872, after the general election but before the Electoral College met to count its votes. Greeley carried no states and won no Electoral College votes. <https://en.wikipedia.org/wiki/1968_Democratic_Party_presidential_primaries#March:_New_Hampshire,_Kennedy_enters,_Johnson_declines https://en.wikipedia.org/wiki/1968_Democratic_Party_presiden...> <https://en.wikipedia.org/wiki/Thomas_Eagleton#Replacement_on_the_ticket https://en.wikipedia.org/wiki/Thomas_Eagleton#Replacement_on...> <https://en.wikipedia.org/wiki/1872_United_States_presidential_election https://en.wikipedia.org/wiki/1872_United_States_presidentia...>