The campaign for the nomination began with incumbent President Lyndon B. Johnson expected to win re-nomination for a second consecutive election, despite low approval ratings following the Tet Offensive in January 1968.

In April, Vice President Hubert H. Humphrey joined the race as the establishment candidate; he did not criticize the administration's conduct of the war and avoided the popular contests for delegates.

McCarthy and Kennedy traded primary victories while Humphrey collected delegates through the closed caucus and convention systems in place in most states.

Humphrey would be the last Democratic nominee to be nominated despite not actively campaigning in the primaries until Kamala Harris in the 2024 United States presidential election.

President Kennedy was assassinated on November 22, 1963; Johnson succeeded him with tremendous national popularity amid a wave of mourning and sympathy.

[5] In search of a way out of the dilemma, Kennedy asked speechwriter Milton Gwirtzman to write a memo comparing two offices: 1) governor of Massachusetts and 2) U.S. senator from New York, and "which would be a better place from which to make a run for the presidency in future years?

On the recommendation of General William C. Westmoreland, whom Johnson had appointed to command American troops in Vietnam, U.S. manpower in Southeast Asia expanded from 16,000 in 1964 to more than 553,000 by 1969.

As opposition grew in 1967, anti-war Democrats led by Allard Lowenstein and Curtis Gans formed the Dump Johnson movement, which sought to challenge the President's re-election.

Kennedy continued to demur, despite pressure from his aides to enter the race and worry that anti-war allies, like George McGovern, would begin to make commitments to McCarthy.

The following persons were listed in two or more major national polls or were the subject of media speculation surrounding their potential candidacy, but declined to actively seek the nomination.

Running as an antiwar candidate in the New Hampshire presidential primary, McCarthy hoped to pressure the Democrats into publicly opposing the Vietnam War.

He was boosted by thousands of young college students who volunteered throughout the state, who shaved their beards and cut their hair to "Get Clean for Gene."

Despite his desire to oppose Johnson directly and the fear that McCarthy would split the anti-war vote, Kennedy pushed forward with his planned campaign.

As the year developed, it also became clear that Johnson believed he could secure his place in the history books by ending the war before the election in November, which would give Humphrey the boost he would need to win.

As a result, McCarthy won the popular vote easily, and by the rules in place at the time, all 72 of the commonwealth's delegates were pledged to him on the first ballot.

"[28] The Indiana primary thus marked the first open entry of Kennedy into the field and pitted him against McCarthy and Governor Roger Branigin, a favorite son who had backed Johnson and now impliedly supported Humphrey.

[30] The next day in Cleveland, he delivered prepared remarks entitled "On the Mindless Menace of Violence," elaborating the themes he had addressed in Indianapolis.

[32] Martin urged the candidate to speak out against violence and rioting, emphasize his "law enforcement experience" as former U.S. Attorney General, and promote coordination between the government and private sector to solve domestic issues.

[34] McCarthy, meanwhile, contrasted his approach to conflict of "call[ing] upon everyone ... to be as fully responsible as [they] can be" against Humphrey's ("run[ning] things together indiscriminately") and Kennedy's (a "combination of separate interests ... or groups").

[42] Kennedy declared that the results, where two anti-war candidates collectively earned over 80 percent of the vote, were "a smashing repudiation" of the Johnson-Humphrey administration.

His campaign organization, run by U.S. Congresswoman Edith Green, was not strong and his platform emphasizing poverty, hunger, and minority issues did not resonate with Oregon voters.

The McCarthy campaign responded with charges that Kennedy illegally taped Martin Luther King Jr. as United States Attorney General.

[60] In April and May, Humphrey won the majority of delegates in Delaware, Alaska, Hawaii, Wyoming, Arizona, Maryland, Nevada, New Jersey, Missouri, Maine, and Vermont.

"[68] Though Kennedy considered the debate "indecisive and disappointing," subsequent polling showed that undecided voters favored his performance by a margin of two-to-one.

[70] The campaign entourage and traveling press were all "scared to death," recalled Bill Eppridge, a Life magazine photographer in the car just ahead of the Kennedys.

[71] On June 4, Kennedy privately expressed his hope to Theodore H. White that victories in the California and South Dakota primaries could persuade party insiders that he was more electable than Humphrey and thus win him crucial support from unpledged delegates.

[76] After giving his victory speech at the Ambassador Hotel in Los Angeles, Kennedy was assassinated in the kitchen service pantry in the early morning of June 5.

[62] At the end of June, Republican Senator Mark Hatfield of Oregon assessed the race, arguing that Humphrey would be the party's nominee for president but criticized him for being too closely aligned with Johnson's policies.

[83] Tablemaker's Note:[a] Total popular vote:[148] Johnson/Humphrey surrogates: Minor candidates and write-ins: Primary Map By County (Massachusetts not Included) Hubert Humphrey – Red Lyndon B. Johnson – Yellow (outside of Florida) Robert F. Kennedy – Purple Eugene McCarthy – Green George Wallace – Lime Green Roger D. Branigin – Orange George Smathers – Yellow (Florida Only) Stephen Young – Brown When the 1968 Democratic National Convention opened in Chicago, thousands of young antiwar activists from around the nation gathered in the city to protest the Vietnam War.

In a clash covered on live television, Americans were shocked to see Chicago Police officers brutally beating antiwar protesters.