AMNA NAWAZ: The fact that our country is divided isn't new.

And, in many respects, it can be traced back to the founding of a nation on the promise of freedom, while dependent on slavery, when Black enslaved people couldn't participate in the democracy being created.

Judy Woodruff examines how that foundational contradiction has evolved over time and what it means for our challenges today in her latest installment of America at a Crossroads.

JUDY WOODRUFF: From the ongoing push for equality in schools, in government, and in our communities, to the targeting of communities of color by white supremacists, and the killing of unarmed Black men and women by police..

PROTESTERS: Tyre Nichols!

PROTESTER: Justice for who?

PROTESTERS: Tyre Nichols!

JUDY WOODRUFF: ... America's historic division over race remains at the heart of so many conflicts we see today.

At the Lincoln Memorial honoring a president who held our nation together as that division nearly tore it apart, I met Theodore Johnson, a man who has been wrestling with questions surrounding our history, his own place in it, and the precarious moment we find ourselves in today.

A lot of people would argue that this country is as divided now as it has been at any time since the Civil War.

CMDR.

THEODORE JOHNSON (RET.

), New America Foundation: Right.

JUDY WOODRUFF: Do you see it that way?

THEODORE JOHNSON: I don't.

The Civil War -- Lincoln was the one that said a house divided against itself cannot stand, and he was talking about a nation that was half-slave and half-free.

We're not close to that.

That said, we have got some serious issues that we need to tackle.

And if we don't get it sort of under control, it could spiral out of control and be -- we reach another point in our history where an existential threat is posed by the fact that Americans don't get along with one another.

JUDY WOODRUFF: For years, Johnson has been writing about race, history, politics and democracy, including in his 2021 book, "When the Stars Begin to Fall."

CMDR.

THEODORE JOHNSON: And Us@250 is thinking about 2026.

JUDY WOODRUFF: At the New America Foundation, a center-left think tank in Washington, he's now working on a project examining the country as it approaches 250 years since the signing of the Declaration of Independence.

CMDR.

THEODORE JOHNSON: We have come a long way.

Look, I'm a Black man in America in 2023.

And while things are not perfect, I'd much rather be here than a Black man in America in 1923 or, God forbid, a Black man in America in 1823.

That is a story of national progress.

But that progress was not inevitable.

That progress was the result of people challenging the government.

That progress was the result of protest.

That progress was a result of people giving their lives, their energies, their sweat, giving up their ability to live a peaceful life to fight for the right of future generations to have a better version of America than they had.

JUDY WOODRUFF: Johnson's writing and thinking on these big questions are heavily influenced by his personal history, starting with his maternal great-grandfather, a sharecropper in Southwest Georgia raised during the Jim Crow era.

CMDR.

THEODORE JOHNSON: We called him Daddy Joe.

His name was Joe Humphrey (ph).

And, in this picture, he's at a fair of some sort.

And this is the 1950s.

He's in farming gear, coveralls with, like, his boots polished, pipe hanging out of his mouth.

And behind him are two American flags sort of angled over each shoulder.

And so everything around them told them that this country did not appreciate them, that they didn't belong.

And yet they instilled in their children a faith in America, a faith in hard work, and a belief that, if you just work hard enough, maybe this country won't treat you fairly, but you will make more progress, make more of a way for yourselves and for your families than previous generations.

JUDY WOODRUFF: That promise of progress materialized in Johnson's parents, who were the first in their families to complete college in North Carolina and who later settled there to work for IBM.

CMDR.

THEODORE JOHNSON: And so I grew up like the Cosby kids.

I grew up in Raleigh, North Carolina, in the suburbs mostly surrounded by white neighbors.

But I had no excuse for not doing well here, because of the sacrifices of those who come before me.

And so it's sort of incumbent upon me, I think, to carry that optimism and faith forward.

JUDY WOODRUFF: Johnson attended Hampton University, the historically Black college in Virginia, where he studied mathematics.

Looking for purpose, afterwards, he joined the Navy, where he would go on to serve for 20 years, rising to the rank of commander.

While in the Navy, he worked in national security in the Obama White House and as a speechwriter at the Pentagon for the Joint Chiefs of Staff.

But the questions of his place in this country and his children's became unavoidable.

PROTESTER: No justice, no peace!

JUDY WOODRUFF: The 2012 death of Trayvon Martin, a 17-year-old boy shot to death in Florida for simply walking down the street, was a turning point.

CMDR.

THEODORE JOHNSON: That concern that began in 2012 only accelerated as the years went by because of the increased number of very public deaths of Black men and women at the hands of law enforcement, often caught on camera.

And those videos made their way onto social media at the same time my sons were coming of age, teenagers using social media, and them coming to me with these videos asking me: "Daddy, why does this continue to happen?"

I'm sorry.

And I didn't have a good answer for them.

I could only tell them about the history of our country, the work that people have done to ensure that these things happen less frequently.

But I almost did not have an option, personally, except to change my career, except to leave the military and begin thinking about these issues more seriously.

JUDY WOODRUFF: Johnson returned to school, studying law and policy and earning his doctoral degree writing about the history of civil rights and the Black vote in America.

Now a columnist at The Washington Post, he continues to explore the contradictions he's experienced, reconciling his family history with his own, the promise of America now, with a reality that often falls short.

CMDR.

THEODORE JOHNSON: This ability to hold a love of country at the same time as a sort of critique of the country together, we sort of -- sort of played out on a football field for my family one Friday evening.

One of my sons was playing football, kneeled during the national anthem.

I'm a retired Navy guy.

I was standing at attention during the national anthem.

And, of course, there were some parents around that didn't like the fact that my kid was kneeling.

And I could tell.

It was - - it was pretty audible and clear.

After the anthem finishes, the flag that the team carries out had sort of tumbled to the ground.

And I ran down and picked it up and posted it back up.

And the same folks that were making remarks about my kid kneeling sort of stepped into the aisle to thank me for posting the flag up for them, for respecting the flag.

And, in that moment, my family was still recognizing a pride in country through my sort of standing at attention and a reckoning that the country needs, especially around the question of race, that my son was protesting during the anthem.

And so that seems to be a common strain, not just for me and my family, but for lots of Americans, especially Black Americans, who have served in every war the country has ever had, and yet returned from war to a nation that didn't appreciate them, that didn't treat them as full citizens, that didn't treat them as equal.

JUDY WOODRUFF: You have written about trying to understand why many white Americans are having difficulty with what's happening in our country right now, demographic changes, the fact that more minorities are serving in roles of leadership in our country.

What are you finding out as you try to understand that?

CMDR.

THEODORE JOHNSON: Yes, so here's how I think about it.

When you are raised in a country that tells you that you are the descendants of a remarkable set of men that created a new country on the idea of equality and liberty and justice and democracy, and you're very proud of that heritage, and then, suddenly, people come along and say, wait a minute, that story is not complete.

We were part of that story too.

And not only are they insisting to be part of the story, but now, through demographics, through elections, through economics, they're acquiring more power that they didn't have in earlier versions of America.

This is a status loss.

And it feels very much like any other kind of loss, like losing money or losing any sort of physical security.

It doesn't necessarily mean that they hold racial hatred, or that they despise other folks.

But it does mean that sense of loss will often cause some kind of backlash to sort of ensure that their stability of identity, of history, of heritage isn't interrupted.

JUDY WOODRUFF: Back at the Lincoln Memorial, a reminder of this country's willingness to tear itself apart over these questions.

I asked Johnson how he sees us getting through this moment.

CMDR.

THEODORE JOHNSON: I think the pursuit of it is more important than arriving there.

I don't know that we will ever get to a place where the ideals that are laid out in our Declaration and in the Constitution have been fully achieved.

Perhaps I have read that some have called America maybe the ultimately unachievable project.

It may not be possible for us to live in a democracy this large, this diverse where all of us are created equal, but not pursuing that is the death of the American idea, is the death of what the country could be.

And when we give up the going together, and this -- the hyperpartisanship, the culture war stuff is breaking up our ability to go together, not only will we never get there.

We won't even be on the same journey together anymore.

And when that happens, if history is any guide, political violence is likely to follow, and the dream, the potential of the American experiment perhaps lost.

JUDY WOODRUFF: The view of one man who sees the progress that's been made and who hopes it will continue.

For the "PBS NewsHour," I'm Judy Woodruff in Washington.