The following is gleaned from
an article in Slate that summarizes the primaries from 1972 when the current primary system began.
1972:Sen. George McGovern overcame a "stop McGovern" movement to win the nomination on
June 21.1976: After Henry Jackson withdrew from the ace, Jimmy Carter faced sudden primary challenges from Frank Church and Jerry Brown who entered the race in
May. Carter finally won the nomination on
June 15.1980: Carter was challenged by Sen. Edward Kennedy, who refused to withdraw even when Carter had enough delegates to give him the nomination. Kennedy took it all the way to the convention, finally giving in at the convention itself.
1984: Sen. Gary Hart challenged Walter Mondale. Hart, with far fewer delegates, didn't quit until
June 25.1992: Bill Clinton finally won the nomination in
June.More recent primary history:The two most recent candidates managed to avoid protracted primary fights. Still:
Al Gore: Bradley didn't bow out until March 9
John Kerry: John Edwards dropped out March 3.