1968 was a tumultuous year in politics. Johnson, the sitting President, declines to seek re-election after the primaries have already begun. His VP, Hubert Humphrey decided to give it a shot. Too late to enter any primaries, counting on the convention to grant him the nomination.
Six months earlier, in November of '67, Minnesota Senator Eugene McCarthy entered the race to defeat Johnson for the Democratic nomination. His was an anti-war candidacy and the punditry dismissed him, saying he would have little impact on the outcome of the election.
The Tet Offensive at the beginning of 1968 gave his candidacy legitimacy and he came so close to defeating Johnson in the NH primary that Johnson decided his time was done.
After a disastrous debate ahead of the California primary, the energy started shifting the the recently entered Robert F Kennedy. He took the debate and won the California primary and was then gunned down.
By the time of the convention, the mantle was indeed handed to Humphrey. Even though McCarthy had won the most primary votes, Democrats hoped that a Humphrey presidency would correct the Kennedy-Johnson trajectory.
Republican Richard Nixon took the election by an electoral college landslide but with only 43% of the popular vote. Humphrey got 42% of the vote. Third-party candidate George Wallace got just over 13%.