This traditional approach was criticized by the other candidates, who hoped to win the nomination from popular support.
Late in 1967, building upon anti-war sentiment, Senator Eugene Mc Carthy of Minnesota entered the race with heavy criticism of the President's Vietnam War policies.
His aides Max Kampelman and Bill Connell began to set up an organization and held meetings with Humphrey and his advisors, encouraging him to start a campaign.
Humphrey set up offices for preparation, and unsuccessfully courted Larry O'Brien as campaign manager.
Even before Mc Carthy's entrance, Johnson grew concerned about a challenge.
He confided to Democratic Congressional leaders that an opponent could pull the support of Martin Luther King, Jr. Benjamin Spock, defeating him in New Hampshire, and forcing his withdrawal from the race; similar to Senator Estes Kefauver's 1952 challenge to President Harry Truman, which likely caused Truman not to seek re-election.