Humphrey entered the race too late to participate in any primaries , and relied on " favorite son " candidates to help him win delegates . He also lobbied for endorsements from powerful bosses within the Democratic Party , which provided him with necessary delegates . This traditional approach was criticized by the other candidates , who hoped to win the nomination from popular support . Robert Kennedy was assassinated in June 1968 , leaving McCarthy as his only opponent , until the 1968 Democratic National Convention , when Senator George McGovern of South Dakota ran as the successor of Kennedy . Humphrey won the party 's nomination at the Convention on the first ballot , amid riots in Chicago . He selected little-known Senator Edmund Muskie of Maine as his running mate
assassinated in June 1968
Assassination of Robert F. Kennedy
Hubert Humphrey 1968 presidential campaign