Vice President Kamala Harris’s campaign has been on a roll—stacking up key endorsements and shattering fundraising goals—ever since she emerged as the consensus Democratic nominee for president on July 22. 

Her momentum seems likely to persist through the Democratic National Convention, which begins on Aug. 19. 

But if she is to maintain her momentum after the convention and attract additional voters to her cause, she will need to lay out a clear vision of what a Harris Administration would stand for and the policies she would pursue. It will be a tricky maneuver, especially if those policies diverge from President Joe Biden’s.

History suggests that an incumbent vice president seeking the White House can be hamstrung by a president who has exited the race. Hubert Humphrey faced that challenge in 1968 after President Lyndon Johnson decided to forego reelection largely because of the ongoing and unpopular Vietnam War. Humphrey needed to distance himself from Johnson on the war, but doing so created friction with the president and proved difficult. 

These events have shaped the current conversation about Biden’s withdrawal, but the more instructive episode for the present moment came four years earlier, when Johnson was thrust into the spotlight at a moment’s notice. Johnson’s success at shedding the image of a discounted and frequently maligned vice president and scoring a record-setting presidential election victory illuminates why mapping out a program and a vision that can energize the Democratic base—while also appealing to independents and some Republicans—is so critical.

The circumstances that landed Johnson in power were abrupt and tragic. Riding two cars behind President John F. Kennedy in Dallas on Nov. 22, 1963, Johnson found himself on the floorboards of his limousine after shots rang out in Dealey Plaza. Roughly two hours later, Johnson took the presidential oath of office on Air Force One, with Kennedy’s body in the back of the plane and his widow by Johnson’s side.

The horrific events of that afternoon transformed Johnson, who had been estranged from Kennedy’s inner circle and despondent in a job with little power. Before assuming the vice presidency, Johnson had been arguably the most successful Senate Majority Leader in history. But as Kennedy’s number two, Johnson had been consigned to symbolic foreign travel, stewardship of the country’s space effort, and leadership of a toothless presidential committee on equal employment opportunity. He was the butt of jokes, cast aside by Attorney General Robert Kennedy—the President’s younger brother and Johnson’s arch-nemesis—as well as by John Kennedy’s inner circle.

There was even speculation that Kennedy might dump Johnson from the ticket in 1964, with Johnson himself musing about throwing in the towel. In short, he was miserable.

But the tragedy in Dallas, in Johnson’s home state of Texas no less, changed everything.

Johnson grabbed the reins of power, led the country through its period of mourning, and passed bills on taxes, foreign aid, and civil rights that Kennedy had introduced before his murder. In fact, Johnson grasped the possibility of going far bigger than his advisers recommended, or than his predecessor had imagined was possible. Responding to pleas that he sidestep legislation on civil rights, Johnson countered, “Well, what the hell’s the presidency for?” In fact, he labeled Kennedy as “too conservative” for his taste and pledged a more dramatic expansion of the welfare state.

Within six weeks of assuming the presidency, he had announced a “War on Poverty” and committed the state to funding improvements and opportunities in education, jobs, health, and housing. And less than five months later, he articulated the much grander vision of what he called his “Great Society,” a sweeping effort to combine national prosperity with social equality.  That vision of a more compassionate, just, and equitable society, as well as early victories on key pieces of legislation, propelled Johnson to a landslide electoral triumph in 1964. It was a remarkable turnaround for a political figure once consigned to the wilderness. 

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