The following is a transcript of the interview with former special presidential envoy Brett McGurk that aired Sunday, Jan. 20, 2019, on "Face the Nation."

MARGARET BRENNAN: We'd like to now welcome Brett McGurk. He was President Trump's envoy to the global coalition fighting ISIS, but he resigned last month in protest following the president's decision to withdraw from Syria. In an op-ed this week, he warned America's decision to pull out is giving the terror group new life. Brett, thank you for being here.

BRETT MCGURK: Thanks for having me Margaret.

MARGARET BRENNAN: The vice president sat here and reiterated that ISIS is defeated. Is he correct?

BRETT MCGURK: Well they're not defeated. I've been- I've been part of this campaign for four years across two administrations. We've come a- an extraordinarily long way. And in 2014 this organization controlled territory of eight million Syrians and Iraqis. It was committing genocide against Christians and Yazidis and minority groups. It was planning attacks against us in the homeland. It was carrying them out in Paris, that killed Americans in Brussels and Paris. We've come a long way. We have taken away a lot of their physical space but we always said and our policy was, until most recently, we had to make sure that we completed the enduring defeat of ISIS. What that meant was taking away their physical space and retaining a presence so they could not resurge. And what just happened, was that policy was really just reversed overnight. So as a leader of the coalition we've been telling our partners on the ground and around the world, we've built a coalition of 75 countries, that we were prepared to stay in Syria for some time. And on instructions from the White House, we were telling them, we'd stay in Syria until we completed the enduring defeat of ISIS, not just the physical territory. We'd stay in Syria until the Iranians left Syria and also until there was a irreversible political progress in Geneva to end the ultimate civil war. We had told that to our partners on the ground. We had told that to our coalition partners and it was reversed in a conversation between the president and a foreign leader. Leadership- American leadership really counts. Leadership built this coalition. It led to these gains against ISIS. And leadership requires some presence on the ground and also consistency. And it was the total reversal of our policy that made it- I just I concluded I could not be effective in carrying out those new instructions.

MARGARET BRENNAN: We should point out, you joined the State Department under President Bush. You then served under President Obama and then under President Trump. Can you clarify there, I point that out because you serve Democrats and Republicans. Why did you resign specifically?

MCGURK: Well again look I- look--

MARGARET BRENNAN: The President has alleged it's political.

MCGURK: Well I've- I've served all three administrations. I've worked on policies that I fully supported. You work on policies here in the government that you might not support. You argue your case. In this case, I think the entire national security team had one view, and the president in a conversation with President Erdoğan just completely reversed the policy. You know the president has said, I think he's right, you never- you never telegraph a punch when you're in a military campaign. You also don't telegraph your retreat. I've probably traveled to Syria more than any other American civilian official. I know our people in Syria. I- my heart is broken and we're all- our thoughts are with the families and loved ones that were just killed. In this campaign in Syria since 2015, we've had two Americans killed in action. We built this campaign plan, to answer for those who believe that we should not be over invested in these confl- conflicts. Americans are not fighting. We built a force of 60,000 Syrians to do the fighting. American taxpayers are not spending money on civilian stabilization or reconstruction costs. The coalition is doing that. So it was a sustainable campaign plan and we had in- the pieces in place, as we defeat the physical caliphate, to begin a very serious negotiation with some pretty hostile actors in Syria, including Russia. And we had worked with the Russians diplomatically basically to draw lines on the map at the Euphrates River and we said, "Look you don't cross that river. If you cross that river we'll kill you."

MARGARET BRENNAN: And we- have we have a map we can put up just so people understand that what you're saying is- is actually having a real world impact on the ground what President Trump did. And possibly lose the territory that the U.S. has cleared out?

MCGURK: Well the minute you say- the minute you announce to the world that you're leaving, a vacuum opens up and all the other powers in the region start making different calculations. And we have to work things out in Syria with Russia, and our presence on the ground matters. And the two to three thousand Americans we have on the ground are not just any American soldiers. They are our most elite, most highly trained forces. Again I visited them from the beginning of the campaign- I was one of the first civilians on the ground way back in the battle of Kobanî. They have done an incredible job. It is those forces that allow the force of the Syrian Democratic Forces with 60,000 Syrians that we have helped build and enable, they allow that force to be effective. If you simply pull out American forces without a plan for what comes next, it is going to open up a signif- significant vacuum. I know the vice- vice president said we're gonna look for coalition partners to take our place. As the former leader of the coalition, I just don't think that that is credible. I know what it takes in these coalition capitals for them to put their blood and treasure on the line with us. It takes American leadership and takes American presence. And we've just told the world that we're no longer going to be present. So it'll have a dramatic ramification. And that's why, what I wrote in the Washington Post, I think we have to really accept some hard truths. I think number one we are leaving. The president has made that clear- we are leaving. And that means our force should be really with one mission: to get out and get out safely. We cannot add additional missions onto our force while they are trying to withdraw under pressure, because withdrawing under pressure from a combat zone is one of the most difficult military maneuvers we can ask our people to do.

MARGARET BRENNAN: And I think what you're sketching out here is- to put it plainly- how we withdraw. Accept that the president's mind- mind is made up. But one of the issues you have here is that the way the president is doing this puts forces at risk and puts the gains at risk. Am I hearing you correctly?

BRETT MCGURK: Announcing you're going to withdraw, and without a plan, and believe me there's no plan for what's coming next. Right now we do not have a plan. It increases a vulnerability of our force. It increases the environment on the ground in Syria. This environment in northeast Syria has been fairly permissive and safe. Again, I've been there almost 20 times and we have been- been very careful with this. It is increasing the risk to our people on the ground in Syria and will open up space for ISIS. But what's most important is we cannot expect a partner such as Turkey to come in and take our place, or another coalition partner to take our place. That is not realistic. And if our forces are under order to withdraw, as at the same time they are trying to find some formula for another coalition partner to come in, that is not workable. That is not a viable plan.

MARGARET BRENNAN: So when the secretary of state says the U.S. military can strike ISIS or any threat in Syria from anywhere, you're saying that's not actually the case? Being on the ground matters.

MCGURK: Well having a presence on the ground is a critical force multiplier that has allowed us to defeat ISIS as a physical- physical space. To give us the intelligence to keep pressure on them and pulling out all of those forces will have very significant repercussions which we need to be ready for.