Zalmay Khalilzad, who served as George W. Bush’s ambassador to the United Nations, is best known for his role as a diplomat in the Muslim world. As an envoy and ambassador to his native Afghanistan after 9/11, and then again as ambassador to Iraq from 2005-2007, Khalilzad witnessed both countries during eras of unrelenting violence. He is the author of a new book, The Envoy: From Kabul to the White House, My Journey Through a Turbulent World.

Khalilzad was in the news last week for another reason: He introduced Donald Trump before the candidate’s big foreign policy speech in Washington, D.C. In his introduction, he called Trump a “provocative voice” whose message has “resonated” with many voters. And although he has not endorsed Trump, he believes the candidate should be taken seriously. We spoke on the phone about America’s errors since 9/11, Trump’s anti-Muslim comments, and whether he would ever vote for the businessman. The conversation has been edited and condensed.

Since 2001, you have called for a very active American role in the world. Have your opinions changed about what America can or should do in terms of trying to mitigate what you call a “crisis of civilization”?

Sure. I think the lesson I learned from our response to the Soviet invasion of Afghanistan—although I supported the opposition to the Soviet occupation—was that we should not assume what the outcome should be for complex processes. We had assumed that the Soviets would win, and to our surprise, they didn’t, and they left. It left the problem of Islamism as an outcome. We should have remained engaged and helped put Afghanistan together, and if we had done that we perhaps would not have had the rise of al-Qaida and the Taliban, which disengagement produced. While our engagement had some success, our disengagement had more catastrophically negative consequences.

How do you look at Iraq now?

We made some mistakes when we went in. We also made a mistake with how we disengaged at the end. The lesson that I learned is that when we take on projects like Iraq or Afghanistan, we have to recognize it is very costly, and will take a long time, and that therefore we should do it extremely rarely. We have to be very selective.

You said earlier that we should be wary of interventions where we don’t know the outcome. We certainly didn’t know the outcome in Iraq.

Right, but we shouldn’t do things that make the problem worse when we get involved, and in Iraq we made the problem worse. And once we withdrew we created a vacuum.

What do you make of the rise of ISIS?

I was in Iraq when we thought we were making progress on the fight against al-Qaida in Iraq. But the polarization came back. The analogy in my way of thinking is that ISIS are like mosquitoes, and the swamp that produces the mosquitos is a civilizational crisis and the regional rivalry. Without addressing those, we could be doing this anti-terrorist operation for decades more.

Who are we in this analogy, if ISIS is the mosquitos?

We are the anti-mosquito spray. But the swamp keeps producing mosquitoes.

Maybe the spray is leading to environmental consequences worsening the swamp.

Right, that is the unintended consequence, but what do we do about the swamp?

What did you make of Trump’s speech?

Well the speech was an evolution—not a big change—in his stance on some issues, to make himself more in the mainstream of U.S. policy. He did himself some good, but it was far from a foreign policy I could endorse or support. There were some issues that were incoherent, and some issues were wrong. For example, I think no national building under any circumstance is the wrong lesson from Iraq.

You are responding as if it is a serious speech that had some problems.

Right, sure.

Do you take him seriously?

I do take him seriously. I think he is a very shrewd operator, a shrewd guy, with the success he has had. He knows better than some of his rivals what to say and what to do. I think he will adapt further. I would not dismiss him.

I am not dismissing his electoral strength in the Republican Party. I meant as a thinker.

Well, listen, if that was our standard, I don’t know how many presidents we have had that could meet it.

You don’t think Trump is different than the presidents we have had in some fundamental way?

I think intellectually he is not the least capable person who would become president. I don’t think he is less intellectually capable than some people who have been president.

Such as?

[Laughs.] Well I don’t want to get myself in any further trouble.

Well, OK—

I frankly think we should not underestimate him.

I get that. It’s just that sometimes when I talk to Republicans in Washington, I feel a little like I am in a Twilight Zone episode. You have done foreign policy all your life, you know about the world, it seems like you must know that deep down this guy is a dangerous demagogue who cannot be president.

Was he my candidate, my preferred choice? No. But I think if he becomes the nominee then he will have a shot at possibly becoming president and we ought to take him and his views seriously.

Right but maybe he would have less of a chance of becoming president if people were speaking out against him more.

I agree with that. People should, where they differ. I am all in favor of that. A clash of ideas and solutions is what elections are about. And once the election is over we need to come together. I was pleased that he said he would pursue a bipartisan foreign policy if he became president. I think he is evolving.

Could you vote for him?

Not today I couldn’t, no, but we have to see what happens.

So when he says he would have a bipartisan foreign policy, you take that at face value?

I don’t know him well. I met him the day I introduced him. But those who know him well say that he is quite pragmatic and he will adapt. And that as CEO he will surround himself with people and hold them accountable.

Like his campaign manager who grabbed a reporter and is still on the job?

No, no, no, I am talking about business people.

I was referring to holding people accountable.

Oh, I see what you mean. I am not making the argument, I am saying that people who know him talk about him like that.

What did you make of him when you talked to him?

It was a reasonable conversation about the campaign and about the speech and what I might say in my introduction. It wasn’t a long conversation. It was in the nature of chit-chatting.

I read you were the highest-ranking person to serve as a United States diplomat who is Muslim. Is that true?

It is true.

Did you talk to Trump about serving the United States as a Muslim diplomat and his comments about Muslims?

He was told that beforehand. We didn’t get into my religious identity.

I didn’t mean about your religious identity. I meant his comments.

No we didn’t talk about Islam. But I had said to him through an intermediary that I would respond if he denounced Islam.

But he has said things.

He has said it before, but not in the speech. In the speech he talked about our Muslim partners, wanting to work with them.

No dipping bullets in pigs’ blood?

[Laughs.] That’s what I was worried about, and I would have responded to that, or if he said Bush had lied.

You know how these guys work, they say different things to different audiences.

Isn’t that called politics?

I am not sure everyone does it quite this way.

Unfortunately I know too many who tend to do that.

The sense I am getting from you is that you might not necessarily support Trump but he isn’t someone you see as far out of the mainstream.

Right. He should not be dismissed. I am old enough—and I don’t want to give the sense that I am comparing them—to remember when people said Ronald Reagan was a B-level actor who could only read his lines and who had an empty head and a nice suit and who would cause a nuclear war because he was so irresponsible. And now we think he was one of our greatest presidents.

Read more Slate coverage of the 2016 campaign.