An aging Democratic president who rose to prominence in the Senate announces his withdrawal from the race. The party is rived by ideological clashes and an anguishing war overseas. A notorious Republican rides a reactionary swell to threaten a Democratic winning streak. And a Chicago convention, scheduled for August, promises to be a staging ground for both hope and rancor.

The parallels between 1968 and 2024 are uncanny. Joe Biden has become the first president since Lyndon B. Johnson to forgo seeking another term — and Kamala Harris, like Johnson’s vice president, Hubert Humphrey, has been elevated without having won any mandate in party primaries. There will be protests in Chicago, just as there were in ’68: Instead of Vietnam, this year’s will center on Israel’s war in Gaza, which the left blames on Biden’s support for the government of Prime Minister Benjamin Netanyahu.

There are, of course, vast differences. Democrats are far more united behind Harris than they were around Humphrey; there will be no contested convention this year, no war for delegates. And Richard M. Nixon, a darkly introspective child of the working class, was not Donald Trump.

And there is another overlooked divergence: Today’s left does not have leaders to dominate the discourse — or even its own movements.

In 1968, the protest movements that challenged Humphrey had names, faces, figureheads. Today there are no Tom Haydens, Abbie Hoffmans or Jerry Rubins headed to Chicago. There are no activists gaining fame via organizing, the way DeRay Mckesson did during Black Lives Matter demonstrations or Tamika Mallory and Linda Sarsour did before the 2017 Women’s March. The two most celebrated political leaders of the progressive left, Senator Bernie Sanders and Representative Alexandria Ocasio-Cortez, fully supported Biden; they did not, as Eugene McCarthy did in 1968, try to wage a primary challenge. Dissent will come in Chicago, but it is challenging to find a single widely known figure, inside the convention or out in the streets, who will be leading any protests.