AMNA NAWAZ: For a perspective on the state of the conflict with Iran, we turn now to Robert Kagan, senior fellow at the Brookings Institution and a contributing writer for "The Atlantic."

Welcome to the "News Hour."

Thanks for joining us.

ROBERT KAGAN, Contributing Writer, "The Atlantic": Thank you.

AMNA NAWAZ: So, for context here, just so folks know who we're hearing from, I want to point out you were co-founder of a neoconservative think tank.

You advocated for years for U.S.

intervention in Iraq, so you're not averse to U.S.

intervention abroad.

But I want to point people to what you wrote in "The Atlantic" in your latest piece about Iran.

You said: "This conflict has revealed in America that is unreliable and incapable of finishing what it started.

Defeat for the United States, therefore, is not only possible, but likely."

Why are you so sure of that defeat?

ROBERT KAGAN: Well, I just don't see what options Donald Trump has or is willing to undertake in order to open up the strait.

And if Iran ends this conflict, as it currently is, in control of the strait, it really completely changes the situation in the Gulf.

It puts Iran in the driver's seat.

It gives Iran enormous leverage, not only in dealing with the United States, but in dealing with the rest of the world.

If Iran can charge tolls, if Iran determines who gets in and out of the strait and when, that's just enormous power.

And, in fact, I think it's even more power than they would have if they were able to develop a nuclear weapon.

And I don't see what option Trump has to solve this problem, because they bombed Iran very effectively for 37 days.

They took out the entire leadership, and yet Iran has never made a concession, and the administration has never been able to do anything to open the strait.

So I think the option that would be necessary would be a full-scale invasion of Iran if you really wanted to remove the regime and open the strait.

I don't think Donald Trump or the American people want to do that.

AMNA NAWAZ: So when you hear the Israeli prime minister, for example, say the war is not over, you hear the president and his Cabinet repeatedly not rule out military action to reopen that strait, what else do you think could be achieved militarily by the U.S.

and Israel right now?

ROBERT KAGAN: Well, as I say, it's not clear to me what.

The United States does not have the capacity without a fundamental change on the ground in Iran, I believe, to open the strait.

Iran will be able to fire at it from all kinds of distances.

And the United States can't possibly protect every ship in the strait with what it has.

So I think it takes much more.

I think, by the way, I'm not surprised that Bibi Netanyahu is saying this.

I think this war has the potential of ending in a very disastrous way for Israel precisely because the leverage in the region and the influence in the region is going to shift away from the United States and Israel and toward Iran and its supporters.

AMNA NAWAZ: Let me bring you back to where we are now with hoping or President Trump saying there could be concessions from Iran or some cease-fire moving forward.

President Trump likes to talk about who holds the cards in these negotiations, right?

He's repeatedly messaged that the U.S.

could resume some kind of bombing campaign,as you mentioned, that was very effective in the early days of the war.

In your view, is that threat of a continued military campaign, is that enough to incentivize Iranians to make some kind of concessions?

ROBERT KAGAN: Well, clearly the answer is no.

I mean, the proposal that the Iranians just sent back in response to the negotiations, I would say, was a slap in Trump's face.

I don't blame him for not wanting to take it.

They're basically asking the United States to pay war reparations and lift sanctions and allow the Iran formally to control the strait.

So that is not the response that comes from a nation that's afraid of further attacks.

I would say, if you just look at the situation objectively right now, the nation that is more afraid of starting the war up again is the United States, not Iran.

And Trump has shown, despite all his big threats about destroying Iranian civilization, even when Iran violated the cease-fire by attacking American ships, Trump only responded by going after where the attack was coming from.

He did not launch any larger attack on Iran.

So it's not inconceivable that Trump could order military action again.

But I don't think the Iranians believe, A, that he actually is going to, or, B, that it would be effective if he does.

AMNA NAWAZ: You said now that defeat for the U.S.

is likely.

America, as you know, in history does not say that it has lost wars.

It hasn't said that in Vietnam or Afghanistan or anywhere else.

What, in your view, is the best possible option for the United States right now?

ROBERT KAGAN: Well there is no good option.

I don't -- again -- and I'm not advocating this, but I think the only military solution would have to be a land invasion that removes the Iranian regime from power.

And since I don't think the United States is going to undertake that, I don't really know what the answer is.

Sometimes, there isn't an answer.

There doesn't have to be a solution.

In fact, one of the things that I'm suggesting in the article is, Americans are not -- in all these other defeats that you mentioned, the United States was actually able to -- they didn't have that much impact on the global strategic situation.

And in some cases, the United States was able to undo some of the damage.

I'm just not seeing here how the damage can be undone, absent the kind of war that I don't think we want to fight right now.

AMNA NAWAZ: When you talk about the damage outside of the region for the United States and the place it holds in the world, what are you talking about there?

ROBERT KAGAN: Well, first of all, this is all taking place in the context of the Trump administration destroying all our alliances around the world.

We have effectively destroyed the NATO alliance.

Trump has made it clear that he's not interested in supporting our European allies, and therefore our European allies are going in a different direction.

I think that we're going to see the same thing in East Asia, if we're not already seeing it.

The Japanese and the Koreans are paying an enormous price.

They're almost entirely dependent on this energy supply, and they're going to have to start figuring out how to look out for themselves.

So there is a big general global breakdown, but specifically in the case of the Gulf, the United States used to be hegemonic in the Gulf, and a lot of nations depended on the United States being supreme in the region and capable of enforcing a general peace.

The United States has now demonstrated not only that it cannot, but that it is not -- it can't be really trusted to make sound strategic judgments.

So I think even the countries of the Gulf which have been dependent on the United States are going to have to look elsewhere.

And so the net result is a real diminishing of American global influence and unmistakably the increase in influence of China, first and foremost, but also Russia.

They are the biggest beneficiaries, to some extent, other than Iran, of the war so far.

And I say that in full consciousness of the fact that Iran has suffered terribly, but even so it can emerge from this war and I think is going to emerge from this war stronger than before the war began.

AMNA NAWAZ: That is Robert Kagan with the Brookings Institution joining us tonight.

Thank you so much for your time.

We appreciate it.

ROBERT KAGAN: Thank you.