AMNA NAWAZ: President Biden will soon land back in the United States after traveling to three European countries in five days.

His last stop today, after two days of NATO meetings, was the newest alliance member, Finland.

White House correspondent Laura Barron-Lopez traveled with the president.

LAURA BARRON-LOPEZ: For Finland, a new era of security against Russian aggression, an era Finnish President Sauli Niinisto credited in part to the work of President Joe Biden.

SAULI NIINISTO, President of Finland: And I have to tell you this week in Vilnius was very impressive to experience the way you created unity.

LAURA BARRON-LOPEZ: Fresh off the NATO summit in Vilnius, Biden paid visit to the newest NATO member and Russia's next-door neighbor.

JOE BIDEN, President of the United States: I have been doing this a long time.

I don't think NATO's ever been stronger.

LAURA BARRON-LOPEZ: Finland broke decades of official military nonalignment when it joined NATO in April, taking a clear stance against the Kremlin after Vladimir Putin's invasion of Ukraine.

On Thursday, President Biden called Putin's war a failure and spoke forcefully about Russian threats to more than Ukraine.

JOE BIDEN: First of all, they have already interfered in American elections, so that would not be anything new.

LAURA BARRON-LOPEZ: That was a stark contrast to his predecessor, who stood in the same room in Helsinki nearly five years ago today.

Then, former President Donald Trump stunned the world when he aligned himself with the authoritarian leader, doubting the U.S. intelligence community's determination that Russia interfered in the 2016 presidential election.

DONALD TRUMP, Former President of the United States: They think it's Russia.

I have President Putin.

He just said it's not Russia.

I will say this.

I don't see any reason why it would be.

LAURA BARRON-LOPEZ: The world has changed dramatically since then, Russia's war on Ukraine posing an historic challenge to the NATO alliance.

More than one year in, the coalition has held and expanded.

NATO pushed through the fastest ratification in modern history for Finland, which applied for membership within weeks of Putin starting the war.

Its neighbor, Sweden, will soon follow.

JENS STOLTENBERG, NATO Secretary-General: He went to war because he wanted less NATO.

He's getting more NATO.

LAURA BARRON-LOPEZ: It is a significant strategic gain for the security alliance.

The Scandinavian country shares the longest European border with Russia, stretching over 800 miles, and its entry more than doubles NATO's total border with its adversary.

Today, President Biden convened five Nordic nations, including Finland and Sweden.

He made his affection toward the region known as they built on NATO talks.

JOE BIDEN: If we left the important decisions to the Nordics, we'd all be in good shape.

LAURA BARRON-LOPEZ: They each spoke of common values and their shared challenges, including climate change.

METTE FREDERIKSEN, Prime Minister of Denmark: You have said before that we have been front-runners on the green transition, but it's you who have brought U.S. back on the green agenda fighting climate change.

LAURA BARRON-LOPEZ: At the end of his European tour, focus shifted back home.

President Biden was unequivocal about the endurance of U.S.-NATO leadership, despite a volatile and divided Washington.

JOE BIDEN: And as sure as anything can possibly be said about American foreign policy, we will stay connected to NATO.

LAURA BARRON-LOPEZ: A clear and decisive end to a briefly tense, but ultimately successful trip.

This meeting between President Biden and five Nordic leaders ended with all of them agreeing that they will soon be delivering bilateral agreements on issues such as artificial intelligence, climate change, and their support for Ukraine -- Amna.

AMNA NAWAZ: So, Laura, President Biden is there to celebrate Finland's addition to NATO.

What's the significance of that right now?

LAURA BARRON-LOPEZ: It has major significance, Amna.

The Finnish president said it very explicitly, that President Biden will go down in history as someone who is key to ensuring that Finland joined the alliance and was very effusive in his praise of the president, as were other Nordic leaders, about the work that he has done to keep NATO together.

Now, it's important that Finland is in the alliance, because, again, that ended the history of neutrality that they have had, of military nonalignment, and also very much was important to Baltic states.

When I was in Lithuania, those there talked to me about the fact that it was important to them that countries like Finland and Sweden be admitted to the alliance, so, that way, their collective security could be insured against Russian aggression.

AMNA NAWAZ: And, Laura, President Biden was also asked about this issue of, is he incentivizing Russia to never end their war in Ukraine?

How is he addressing that?

LAURA BARRON-LOPEZ: President Biden was very forceful in saying that the question of Ukraine's NATO membership is much broader than Ukraine when he was asked about this, Amna.

He said that, look, if any country were at war and wanted membership to NATO, they wouldn't get it because of the fact that it could start World War III.

And he was also saying that, ultimately, he believes that Putin has already, that Vladimir Putin, the Russian president, has already lost the war.

Now, that was striking because of the fact that, at the same time he's saying that Putin has already lost the war, Amna, the president still will not define exactly what an end to this conflict looks like.

AMNA NAWAZ: So, President Biden at the summit made a number of promises about short-term and long-term support to Ukraine.

He returns to Washington tonight.

Laura, how does he make sure that he makes good on those promises?

LAURA BARRON-LOPEZ: There are a number of deliverables that the president is going to have to get across the finish line, including those F-16s that were promised to be transferred to Turkey.

Now, the White House has said that wasn't necessarily in exchange for Sweden being able to join NATO.

But, of course, it was key to this deal ultimately getting hatched.

And there has been opposition to those F-16s going to Turkey.

He's going to need to get that through Congress, in addition to more Ukraine security assistance.

And we have seen continued resistance to helping Ukraine in the House among Republicans.

And then there's also the fact, Amna, that looming over all of this is 2024.

And whether it was officials from the United Kingdom or a Finnish reporter today at the press conference asking and essentially posing to the United States this question of how can allies be sure that the U.S. is going to consistently be part of NATO and be willing to help its allies when, if 2024 comes and President Biden ultimately loses, the next president, such as former President Donald Trump, may very well not want to be as forceful in repairing these allegiances and being a part of this alliance?

AMNA NAWAZ: Our White House correspondent, Laura Barron-Lopez, traveling with the president and reporting tonight from Finland.

Laura, thank you.

LAURA BARRON-LOPEZ: Thank you.