GEOFF BENNETT: Thirty-two years ago today, back in 1991, Ukraine issued a Declaration of Independence from the Soviet Union.

But, as we know, today, Ukraine is fighting to be free of Russian attacks and occupations.

Nick Schifrin has the story.

NICK SCHIFRIN: In a country at war, independence is not celebrated, but commemorated.

President Volodymyr Zelenskyy and his wife, Olena, gave thanks to all those killed in the country's existential war.

And they sang the national anthem.

It's titled "Ukraine Has Not Yet Perished," a dark, but determined call to one day celebrate a new independence.

VOLODYMYR ZELENSKYY, Ukrainian President (through translator): Ukrainian children on Ukrainian squares and streets will celebrate the independence of Ukraine.

NICK SCHIFRIN: The only parade today, prizes of war.

Residents of Kyiv walked through lines have burned-out Russian vehicles.

But, still, the war grinds on.

Ukrainian soldiers evacuated residents from a newly recaptured town in Ukraine's south.

Robotyne was obliterated by Russian occupation and the Ukrainian counteroffensive.

Now the blue and the yellow fly atop what used to be a school.

Ukraine also says soldiers landed in Russian-occupied Crimea.

It's a direct challenge to Russian control and President Vladimir Putin's most prized Ukrainian territory.

Today, in Moscow, Putin praised the legacy of the Yevgeny Prigozhin, the one-time-Kremlin-soldier-turned-traitor, who died yesterday in a plane crash the U.S. believes was likely intentional.

VLADIMIR PUTIN, Russian President (through translator): I want to note that these people made a significant contribution to our common cause of fighting the neo-Nazi regime in Ukraine.

NICK SCHIFRIN: But that fighting has caused Ukrainians unimaginable loss.

In the western city of Lviv today, Ukrainians walked through a cemetery that continues to grow.

Ievhenia Demchuk carried her son to his father's grave.

Ihor was a combat medic killed three weeks ago.

They moved here to this city from Central Ukraine to be close to him.

IEVHENIA DEMCHUK, Widow (through translator): We lived for each other.

I have no right to leave him here.

That's why we raised defenders, our boys.

I now have to take care of him by myself.

Today, he turns 2 years old.

Dad was very proud of him.

He called him his little independence.

NICK SCHIFRIN: The U.S. estimates that Ukrainian fatalities and wounded since last February is full-scale invasion to be as high as 150,000, not to mention the millions of Ukrainian civilians who have been displaced, wounded and killed.

For more, we turn to Oksana Markarova, the Ukrainian ambassador to the U.S.

Ambassador, thank you very much.

Welcome back to the "NewsHour."

OKSANA MARKAROVA, Ukrainian Ambassador to the United States: Thank you for having me.

NICK SCHIFRIN: Let's start with the counteroffensive.

And some U.S. officials, to me and two other reporters, have been blunt.

They have been concerned about some Ukrainian military strategic decisions.

These U.S. officials worried that Ukraine is putting too many soldiers in the east, rather than the south, too many Western weapons are going to the east, rather than the south, which is the front of this counteroffensive.

What's your response to those concerns?

OKSANA MARKAROVA: Well, first of all, we have big trust in our military commanders.

I think, since the start of this full-phased war, they have shown that they are very capable, they know what they're doing.

We have been able to liberate more than 50 percent of what Russia has taken since February 24.

And, frankly, I have never heard in the conversations with the officials any criticism.

We all understood from the very beginning that it's going to be very difficult summer campaign.

We knew that the enemy is well-prepared.

We also know that enemy, Russians, do not -- have disregard for any human life.

You have seen what they have done with Robotyne, what they have done with Marinka.

They simply destroy everything within... NICK SCHIFRIN: These are towns that Ukraine has now moved into as part of the counteroffensive.

OKSANA MARKAROVA: Yes.

Yes.

But when our defenders are liberating them, they're trying to be very careful, because they are liberating our people.

So we knew it's going to be difficult.

We knew it's going to take all we have, and it still will require many more capabilities and more weapons.

But we didn't lose any sense as the summer campaign started, and we keep moving forward.

NICK SCHIFRIN: There are some intelligence estimates that fear Ukraine will not reach one of its main goals, Melitopol in the south.

What's your response to that skepticism, that doubt that is inside the U.S. government?

OKSANA MARKAROVA: We have one goal, to liberate all Ukraine.

And we will reach that goal.

Now, how much time, weapons, energy it will take, that's -- of course, nobody knows that.

But I have been recently in Kyiv, spoke with all our commanders.

They know it's difficult, but they also are very optimistic.

And now, with all the new packages that we hear from the U.S. and other allies, hopefully, with more longer distance, we are very eager to train.

NICK SCHIFRIN: Long-distance weapons.

OKSANA MARKAROVA: Yes, we're very eager to train on all the new capabilities and F-16s.

All of that will help us to liberate Ukraine faster.

NICK SCHIFRIN: The U.S. announced today that Ukrainian pilots will be training in the U.S. for F-16s.

Yet the U.S. still does not send some of the weapons that Ukraine is asking for, some long-range weapons known ATACMS.

Does Ukraine have a plan if it doesn't or if it can't reseize all the territory you hope for?

OKSANA MARKAROVA: Well, we have, again, one strategic goal, to liberate all Ukraine.

We have our peace formula plan, which President Zelenskyy is very active, and not only discussing with the leaders, but also we have a number of subgroups on the 10 steps, which have been discussed right now.

And, again, we have focused on the goal.

And we're positive that, if we are all united, and if we do it together, we can reach it.

And, actually, we have to reach it, not for the sake of Ukraine, but for the sake of all of us who believe in the same principles.

NICK SCHIFRIN: The Biden administration uses the term as long as it takes.

But on that united aspect of this, there are some doubters within the Republicans who are just now, as of last night, debating in the Republican primary.

And let me show you one of the quotes from Vivek Ramaswamy, a businessman who's running for president: "We are protecting against an invasion across somebody else's border in Ukraine, when we should use those same military resources to prevent the invasion of our own Southern border here in the United States."

Are you fearful that someone like him or someone who feels that way could become president of the U.S. and reduce support to Ukraine?

OKSANA MARKAROVA: Well it's an internal matter of the U.S. who will become the president.

And, of course, as a democracy, Ukraine welcomes the democratic process.

And it's up to the American people who American people will elect.

What I will say is, I was great -- I was glad to hear yesterday when I was watching the debate that almost everyone else understood very clearly that actually supporting Ukraine is in the U.S. national interests.

If we want to deter other autocrats, if we want to restore the order, which is the basis -- the world order, which is basis for the prosperity for all -- of all civilized world as we know it after the World War II, if we want to send a resounding message that democracies not only can defend themselves, but help each other, and if we want to contain this war, to defeat Russia while it's still in Ukraine, and not to involve other NATO members -- and Putin has been very clear that his threat is to everyone else.

Then it's the right and effective, actually, choice to continue supporting Ukraine so we can win faster.

NICK SCHIFRIN: But -- yes, Nikki Haley, former U.S. ambassador to the U.N., former Vice President Mike Pence did express their support, the establishment candidates.

But the person who wasn't on the stage last night, former President Donald Trump, has also questioned whether he would send aid, as much aid, to Ukraine.

And he's by far the front-runner.

So do you acknowledge that there is some erosion of Ukraine's support among at least part of the Republican Party?

OKSANA MARKAROVA: Well, the majority of Americans, whether Democrats or Republicans, support Ukraine.

We have seen it in all polls.

I see it outside when I walk in Washington, D.C., but also when I travel.

I just recently traveled to Ohio.

Overwhelming support.

People understand -- and American people are not only very generous people, but also people who are brave and free, as your anthem says, people who believe that, when injustice is done somewhere, or, as Martin Luther King said, the threat to justice anywhere is a threat to justice everywhere.

I feel from the American people that they understand it, and they understand how important it is for all of us to win.

NICK SCHIFRIN: Finally, we saw in the story that preceded us the reports of Yevgeny Prigozhin's death yesterday and the U.S. assessment.

President Zelenskyy today said Ukraine was not behind Prigozhin's death, but -- quote -- "Everyone realizes who has a relationship to his death."

Who's that?

OKSANA MARKAROVA: Well, we see war criminals not only attacking Ukraine, but also killing each other on a regular basis.

And, frankly, everyone in Russia, from President Putin, to all the commanders on the battlefield, whether they are commanders and official ministers of defense, or thugs like late Prigozhin, they all are war criminals.

And when they decide to kill each other, it's their internal issue.

But I think it's again showing how fragile and -- Russia is and how this aggressive, senseless war that they have started against Ukraine is actually ruining their regime.

NICK SCHIFRIN: But does Ukraine believe that Vladimir Putin killed Yevgeny Prigozhin?

OKSANA MARKAROVA: Well, if -- when our intelligence will have this information, they will say it.

Of course, I will be more than happy to confirm it.

But at this -- at the moment now, I think nobody knows it for sure.

But we cannot exclude it, of course.

NICK SCHIFRIN: Ambassador Oksana Markarova, thank you very much.

OKSANA MARKAROVA: Thank you.