Chicago has hosted more presidential conventions than any other U.S. city, stretching back to 1860 when Republicans nominated Abraham Lincoln, but perhaps none was as notorious or as consequential as the 1968 Democratic Convention, when deep divisions over the Vietnam War played out on both the convention floor and on the streets of Chicago, that history and its relevance to today is the subject of tonightús installment of Judy Woodruffús ongoing series, America at a crossroads.

MICHAEL JAMES, 1968 Democratic Convention Demonstrator: You know, we thought of ourselves as revolutionaries in those days, and we were really irked by the Democratic Party and the war in Vietnam.

JUDY WOODRUFF (voice-over): Michael James was in Chicago in 1968 when the protests at the Democratic Convention began.

MICHAEL JAMES: Itús not just the war in Vietnam.

It was early womenús movement, certainly civil rights movement.

People were really aware of what was going on in the world, and were taken out of the Democratic Party.

We were demonstrating because all of the delegates were staying here.

JUDY WOODRUFF (voice-over): I met him across the street from the Hilton in downtown Chicago, where he took part in some of the most intense clashes, including when he and others began rocking a police van.

MICHAEL JAMES: And thereús a lot of myths about tipping it over, but we never did.

We rocked it.

This guy in this passenger seat.

JUDY WOODRUFF: Right here.

MICHAEL JAMES: Right here, he comes out.

He grabs one of these guys.

I grabbed him.

I took him down, and I disappeared.

JUDY WOODRUFF (voice-over): It was another violent moment in an already bloody year.

MARTIN LUTHER KING, Civil Rights Leader: Weúve got some difficult days ahead.

JUDY WOODRUFF (voice-over): Civil rights leader Martin Luther King had been assassinated, leading to days of riots in major cities, including Chicago, mired in the Vietnam War, which would kill tens of thousands of Americans.

President Lyndon Johnson decided not to seek a second term.

LYNDON JOHNSON, Former U.S. President: I shall not seek and I will not accept the nomination of my party for another term as your president.

JUDY WOODRUFF (voice-over): He threw his support behind his vice president, Hubert Humphrey, but it was up to the delegates to choose a new nominee at the convention.

Then in June, less than three months before the convention was set to begin, one of Humphreyús challengers, Robert F. Kennedy was gunned down.

RICK PERLSTEIN, Author: The menace of violence was everywhere.

It was inside the convention hall.

It was outside the convention hall.

JUDY WOODRUFF (voice-over): Chicago based author and journalist Rick Perlstein has written extensively about that summer, including in his book "Nixonland: The Rise of a President and the Fracturing of America."

We met at the Chicago History Museum last week.

RICK PERLSTEIN: It all came to a head on Thursday, August 28, when the protesters tried to march to the convention hall from this hotel downtown, were kind of waylaid by the police, so they decided to sit down right in the middle of the street, do a sit down strike right in front of the cameras, and the Chicago Police waded into the crowd with billy clubs and just randomly started beating people as hard as they could, throwing them into police wagons.

When the police wagon was full, theyúd throw a tear gas canister inside, then they would close the doors, and the protesters were chanting, the whole world is watching.

JUDY WOODRUFF (voice-over): The cityús mayor, Richard J. Daley, was incensed by protesters threatening to disrupt the convention.

Police were also angry, feeling they had been held back from responding in full force earlier that year during the riots following Kingús assassination, and many of the protesters thought the country would be on their side.

RICK PERLSTEIN: But it turned out that most of the country seemed to side with the police.

Believe that they must have been provoked.

MAN: With George McGovern as President of the United States, we wouldnút have to have to stop those statics in the streets of Chicago.

JUDY WOODRUFF (voice-over): At the same time, there was chaos inside the convention hall as the party battled over whether to call for the end of the Vietnam War.

RICK PERLSTEIN: That was equally conflict written and all of these forces came together in an extraordinary confluence of violence, anger, and all of it was seen on TV.

JUDY WOODRUFF (voice-over): In the end, Perlstein explained, most Americans sided with the police.

Richard Nixon ran on a promise to restore law and order.

RICHARD NIXON, Former U.S. President: A growing concern is also the issue of peace at home.

JUDY WOODRUFF (voice-over): That November, he narrowly beat the eventual Democratic nominee Vice President Hubert Humphrey.

RICK PERLSTEIN: It was definitely an inflection point, and many, many things, is an inflection point for the Republican politics of law and order and basically presenting themselves as the forces of hierarchy decency.

You know, if youúre behind a white picket fence and work hard and play by the rules, the people Richard Nixon termed the silent majority were for you and the Democrats are in cahoots with these anarchists, right?

It was, you know, profoundly inaccurate.

It was a smear, but that was the beginning of that smear.

JOE BIDEN, U.S. President: I revere this office, but I love my country more.

JUDY WOODRUFF (voice-over): Fast forward to today, when a sitting Democratic president has stepped aside, a conflict rages overseas that has reignited tensions on the left.

There are renewed pushes for womenús rights and racial equality, and the Republican presidential candidate himself, a recently convicted felon facing more charges, is running on a promise of law and order.

RICK PERLSTEIN: I think the parallels donút really rise above the level of the superficial.

Conventions are very different now than they were in 1968 in part because of 1968.

In 1968 the guy who became the Presidential Nominee the Democratic Party didnút enter a single primary.

Basically, the delegates decided who to vote because political bosses told them to.

And these were deals made in back rooms, often at the convention.

JUDY WOODRUFF (voice-over): Following 1968 the Democratic Party reformed its nominating contest to favor primaries giving voters more of a say, while Perlstein says this year is unusual, Harris did appear on primary ballots with President Biden, and since his stepping aside, delegates have overwhelmingly lined up behind her.

But the question remains if younger progressive voters who are pro-Palestinian will also back Harris.

JUDY WOODRUFF: How would you compare the passions that were flowing in 1968 around Vietnam with whatús going on now in the United States, around the Israel, Gaza war?

RICK PERLSTEIN: Well, thereús, you know, considerable group of people who are extremely passionate about whatús going on in Israel and in Gaza.

I would say the biggest difference is that the people who are extremely passionate about what was going on in Vietnam were young people who could have ended up in Vietnam that same month.

And this is a time in which as many as 100 American soldiers were dying a day.

You know, I donút want to take away from a moral passion, but you know, this was kind of life and death.

JUDY WOODRUFF (voice-over): In addition, Perlstein says the federal government now runs security, which has become much tighter, especially after the terrorist attacks of 9/11.

RICK PERLSTEIN: There was this brief shining moment in which, you know, this crazy thing American political convention that is not predictable, seemed possible, but the Democrats are in array.

You know, theyúve lined up behind a candidate.

I think 83 percent of Democrats said that they agree with the decision of the party to put forward Kamala Harris over Joe Biden.

The delegates will vote for her.

Will hear inspiring speeches, will see celebrities sing songs, and life goes on.

JUDY WOODRUFF: But very different from ú68 inside the hall.

RICK PERLSTEIN: Very different from 1968.

America before August 28, 1968 and after August 28, 1968 was a different America.

The idea that this convention will be a watershed is pretty much inconceivable.

Now, this election might be a watershed.

But, you know, the energy lies elsewhere.

MICHAEL JAMES: I think itús important to keep it kind of cool.

JUDY WOODRUFF (voice-over): Thatús a point that Democrat and former 1968 protester Michael James agrees with.

MICHAEL JAMES: I definitely donút want to have what happened in ú68 happen because I think that the danger of having the orange haired guy resume office of presidency will really be a disaster, not only for America, but the world.

JUDY WOODRUFF: For PBS News Weekend, Iúm Judy Woodruff in Chicago.