AMNA NAWAZ: For perspective on the challenges of providing a security guarantee to Ukraine, we turn to James Townsend.

He had a decades-long career focusing on Europe, including as deputy secretary of defense for Europe and NATO policy during the Obama administration.

He's now a senior adviser at the Atlantic Council.

James Townsend, welcome to the "News Hour."

Thanks for joining us.

JAMES TOWNSEND, Former Defense Department Official: It's great to be here.

Thank you.

AMNA NAWAZ: So militaries, as you well know, can be used for offense and for defense.

How can a security force or guarantee be put together that simultaneously provides security to Ukraine, but also doesn't provide Russia with the pretext that it's threatening Russia in any way?

JAMES TOWNSEND: Well, the goal of this coalition of the willing and this security guarantee is to deter Russia.

It's not to threaten Russia.

So the kinds of equipment that this military force could have would not be something that would be seen as good for the offense.

This is something that's going to be instead something that is involving air defense, it's involving some anti-tank weapons, that kind of thing, so that it can't be mistaken as a threat to Russia.

AMNA NAWAZ: We have already heard from Sergey Lavrov of Russia that this idea won't move forward without Russian involvement or Chinese involvement.

If you are Vladimir Putin, why would you agree to any of this right now?

JAMES TOWNSEND: Well, he is truly looking on this as something that will stop him from taking further advantage of Ukraine down the road, that's for sure.

And so he places a high price on having a neutral Ukraine and a Ukraine with a small military force.

But if he wants something bad enough, if he wants a bigger piece of Ukraine or other kinds of concessions from Ukraine or from the West, then he will give in to this, maybe a reduced version of a security guarantee or a force that looks a little bit different.

But if he really wants something else, the price that he will have to pay is having this security force there.

AMNA NAWAZ: So in terms of what he might agree to, what would work for Ukraine, what the NATO nations can provide, as Nick reported, you heard France and Britain say that they're willing to deploy thousands of troops into Ukraine who could help support and train troops in Ukraine, also help to observe any peace deal.

Just give us a sense of what that looks like in practical terms on the ground.

JAMES TOWNSEND: Well, in practical terms, these forces will have to be at a high state of readiness.

They will need to be outfitted with equipment that we were just talking about that are not threatening, but that are going to be successful in terms of making sure Putin understands that they are a credible force and that can be a deterrent to him.

They will need to exercise.

They will need to work with a Ukrainian military force that is also strong.

So Putin can't have his way in terms of having a tiny Ukraine force come out of any agreement.

That force needs to be robust.

And these two countries or other members of the coalition of the willing need to work very well with them, in concert with them to make sure Putin knows that they're going to have a hard time crossing into Ukraine with these forces on the ground.

AMNA NAWAZ: To have a force that is credible, as you say, that is robust, as you say, how fraught is that, though?

I mean, how do those troops, if they end up getting fired at in some way, does the Article 5 collective defense mean that these troops are now part of this larger war?

JAMES TOWNSEND: Well, that's a great question.

And that's what they're working on right now.

The -- this Article 5-like scenario that they're talking about really talks about the nations that are sending these troops into Ukraine, that the understanding would be -- and this is, again, a best guess because we don't know.

But it looks like what they're going to say is that those countries sending in these troops will have to be ready to support these troops, reinforce these troops, give these troops everything they need should the Russians come across the border.

And Putin needs to know that this will happen, that these troops will not go away.

They won't retreat.

Their countries won't come in and pull them out, that, in fact, with this kind of guarantee that if one of those bits of the coalition is attacked, the others will come into their defense, along with Ukraine as well.

AMNA NAWAZ: What about the U.S. role in all of this?

It's being reported today that a senior U.S. Pentagon official told a group of allies that the U.S. will play a minimal role in Ukraine's security guarantee.

Does any of this work without the U.S. acting as a backer?

JAMES TOWNSEND: Well, it can work without the U.S. providing a backstop, but the U.S. engagement is part of the deterrent for Putin.

Putin's got to know that, in fact, the U.S. is part of this.

We may not have boots on the ground.

We may not have combat forces.

A light touch U.S. engagement could be providing transportation.

It could be providing intelligence.

It could be cyber defense.

It could be providing satellite communications, things that the French and the Brits and others who might be in the group don't have as much of as the U.S. does.

So this engagement will be helpful by the United States.

It will help support those that are going to be on the front line.

But it's also a strong signal to the Russians that we haven't walked away, that we're part of this too, and we're going to support that coalition and we're going to support Ukraine as well.

AMNA NAWAZ: James Townsend, senior adviser at the Atlantic Council, thank you so much for joining us.

JAMES TOWNSEND: Thank you.