AMNA NAWAZ: Leaders from all 31 NATO member nations will hold their annual summit next month in Vilnius, Lithuania.

Ahead of that, some members and Ukrainian President Volodymyr Zelenskyy are stepping up their calls for Ukraine to join the military alliance.

Ali Rogin has the details.

ALI ROGIN: Poland's Parliament today passed a resolution supporting Ukraine's admission to NATO.

Ukraine in NATO was a contentious issue long before the war began, and it has only accelerated since then.

We have now our own debate on when or whether Ukraine should be invited into NATO.

Charles Kupchan served on the National Security Council staff during the Obama and Clinton administrations.

He's now a senior fellow at the Council on Foreign Relations and a Georgetown University professor.

And Evelyn Farkas was deputy assistant of secretary of defense for Russia, Ukraine and Eurasia during the Obama administration.

She is now the executive director of the McCain Institute at Arizona State University.

Welcome back to you both.

Evelyn, I want to begin with you.

You support Ukraine becoming a member of NATO now.

Why.

EVELYN FARKAS, Former Defense Department Official: Ukraine has earned it.

First of all, we gave Ukraine a political agreement back when the international community took their nuclear weapons that we would defend them if they were invaded.

And the countries that were supposed to defend Ukraine did defend Ukraine to some extent, but not to the extent that Ukraine expected.

Since then, Ukraine has been fighting to uphold the international order, the principles of the sanctity of borders, which Russia has violated it repeatedly.

And, frankly speaking, they are now the most capable, the largest, most NATO-interoperable, battle-hardened, capable military on the European continent.

So, from a military perspective, they have also earned it.

ALI ROGIN: Charles, to you, what's your response?

Has Ukraine earned it?

CHARLES KUPCHAN, Former National Security Council Official: I'm all for helping Ukraine and doing our best to enable Ukraine to recover as much of its territory as possible, hopefully all of its territory.

But I part ways with Evelyn on the question of whether NATO should open its doors and offer membership to Ukraine at this point.

President Biden and his NATO allies are helping Ukraine defend itself, but they're not going to war to defend Ukraine, in part because they have made a judgment that they're not ready to see NATO go to war with Russia, risk World War III over Ukraine.

And we need to keep in mind that, if NATO does admit Ukraine, and a single bomb were to fall on Kyiv, we would have a treaty-based obligation to go to war with Russia.

Secondly, I think that we see that this is a war that is going to go on for a long time.

We don't know how to -- how it will end.

We need to keep open the prospect for some sort of cease-fire, perhaps an armistice, in which we might need Russia to play ball.

Much harder to get them to play ball.

Two final reasons.

One is, there's no consensus in NATO about admitting Ukraine.

NATO's strongest suit right now is its unity.

And I don't think we want to interject this debate right before the summit in July, and go into that summit with disunity.

And, finally, there's the domestic question.

Sweden is on the path to NATO membership.

Turkey is blocking it.

It's not clear to me that, if we go down the path of wanting to admit Ukraine, that our own Senate would be ready to ratify it.

Before we start moving toward NATO membership for Ukraine, we need to make sure our political ducks are in order.

ALI ROGIN: Evelyn, I want to pick up on Charles' first point, which was that we should not necessarily be ready to commit American troops to this fight.

You have pointed out to us at the "NewsHour" that Article 5 of NATO's principles that states collective self-defense does not necessarily specify what that response looks like.

So, we're not automatically promising troops to the front.

So, are you saying that you believe that is a commitment that the United States should be willing to make at this point?

EVELYN FARKAS: If Russia is allowed to prevail -- and a cease-fire essentially will mean that Putin can rest, his military can regain strength, and it can attack Ukraine again -- if Putin prevails militarily in Ukraine, he will turn to Georgia, he will turn to Moldova.

And then, make no mistake, Putin will challenge the NATO alliance.

He will do something to cause us to have to make a decision about whether we trigger Article 5 or not.

So it's far better to deal with Putin in the Ukraine context and to deter him there from even -- even having the possibility of fighting another day against NATO.

And how do we do this?

Basically, we have a precedent in the Cold War, where East Berlin was part of Germany, but we did -- and West Germany -- but we did not extend Article 5 to that area because it was occupied by Soviet forces.

So there are ways to get around Article 5.

And if Russia were to attack a part of Ukrainian territory where they are not today, meaning the Ukrainian government has control, so, therefore, Article 5 would count, we can then take a decision about what action to take.

And it does not mean that it necessarily has to involve an escalation all the way to nuclear or to all-out war.

ALI ROGIN: But, Evelyn, sticking with you.

How do you make determinations about what parts of Ukraine are Ukrainian and what parts are under Russian control in an active war zone like this, where individual cities change hands every day?

EVELYN FARKAS: Well, I think, if there's any question, then you just put it into the disputed category.

I don't -- I think it's fairly clear day to day with which towns are controlled.

But on the day that Ukraine becomes a member, that's the day that the map counts.

I recognize that it's a little tricky.

And there's a little bit of danger there for those towns on those days right before when a decision is being finalized.

But I think it's a way to work around it.

ALI ROGIN: The Biden administration has indicated that it is not inclined to support NATO membership at this time for Ukraine.

It would want to wait at least until fighting has ceased.

But, today, there are reports that it is open to agreeing to waive the so-called Membership Action Plan, a series of commitments that NATO applicants have to make before they are admitted.

So, Evelyn, to you.

What do you make of that signal from the Biden administration?

And is that enough?

EVELYN FARKAS: I think, Ali, the Biden administration is responding to pressure from the Europeans.

And I think it's the majority of the NATO members.

I was just in Sweden and Finland, heard that they are very much in favor of NATO membership for Ukraine.

So the Biden administration is not leading this time when it comes to Ukraine's NATO membership, as we were in the past.

And so I think the administration is trying to close the gap between us and our European allies.

ALI ROGIN: Charles?

CHARLES KUPCHAN: I would agree with Evelyn.

I think, Ali, that the Americans are looking for something to give the Ukrainians at the summit.

Waiving the Membership Action Plan is not a bad idea, but it's a procedural maneuver that doesn't really change the game.

It kicks down the road the question of, will Ukraine ever get into NATO?

I think, right now, the main line of effort will stay the main line of effort, and that is getting arms to Ukraine, so that they can continue this offensive and take back as much land as possible on the battlefield.

ALI ROGIN: Charles Kupchan, Evelyn Farkas, thank you so much for joining us.

EVELYN FARKAS: Thank you, Ali.

CHARLES KUPCHAN: It's my pleasure.