Transcript for Trump's surprise visit to troops in Iraq

with that breaking news overseas. Lights out and window shades drawn on air force one. That's president trump, describing the secret trip he and wife Melania made to Iraq to visit U.S. Troops. The Christmas night journey, his first ever to a combat zone. The president admitting the 11-hour journey in the dark of night. That unexpected mission to Al Asad air force base winning smiles from the service members on the ground. All of this coming with key changes back here at home. ABC's chief white house correspondent Jonathan Karl leads us off. Reporter: Tonight, a visit by the commander in chief to troops at the Al Asad air force base in Iraq. President trump's first visit to troops in a war zone since taking office nearly two years ago. We came to Al Asad to share our eternal gratitude for everything you do to keep America safe, strong and free. Reporter: Arriving with the first lady, president trump was greeted with a standing ovation by some of the more than 5,000 U.S. Troops now deployed in Iraq. He praised their effort in helping take on ISIS, the terrorist group that its peak some five years ago controlled about 40% of Iraqi territory. Two years ago, when I become president, they were a very dominant group, they were very dominant. Today, they're not so dominant anymore. Reporter: America played a key role in helping the Iraqi army expel ISIS from most of the country. Great job. I looked at a map, and two years ago, it was a lot of red all over that map, and now you have a couple little spots, and that's happening very quickly. Reporter: The president said he would keep U.S. Troops in Iraq, even as he defended his abrupt decision last week to withdraw all 2,000 American troops now deployed in neighboring Syria. Our presence in Syria was not up-ended and was never intended to be permanent. Reporter: For too long, he said, America has been bearing too much of the cost for leading the war on terror and defending our allies. So we're not the suckers of the world. Reporter: The surprise trip, which came in the middle of a government shutdown, was shrouded in secrecy. Military jets escorted air force one on the 11-hour flight that left Washington at midnight on Christmas. I had concerned for the institution of the presidency -- not for myself personally. I had concerns for the first lady, I will tell you, but if you would have seen what we had to go through, with the dark in the plane, with all windows closed, with no lights on whatsoever anywhere. Pitch black, I've never seen that. Reporter: The president spent more than three hours on the ground with the troops, posing for selfies and signing autographs. The christmastime visit to troops coming after perhaps the most chaotic week of his administration. The withdrawal from Syria came as a shock to even his strongest allies. They're all coming back. And they're coming back now. Reporter: That prompted widespread criticism from some of the president staunchest supporters in congress and the resignation of defense secretary Jim Mattis. All right, Jonathan Karl joining us now from the white house. And it is notable, Jon, who the president traveled with, but also, who the president didn't travel with. Reporter: Well, outgoing defense secretary Mattis, who the president is pushing out of office as of next week, was not on the trip. But the president was asked when he intends to nominate a permanent replacement to Mattis, he told reporters he is in no hurry to do so. But Tom, he insisted that, quote, everybody wants the job. Jonathan Karl for us at the white house tonight. Jon, thank you.

This transcript has been automatically generated and may not be 100% accurate.