Transcript for Outgoing White House chief of staff challenges definition of border wall

And in the middle of government shutdown, the white house is losing its chief of staff. John Kelly leaves on Wednesday after 18 months in one of the toughest jobs in Washington. Tonight, he has a surprising new interview about the border wall, and how he believes his success in the job should be measured. Here's Kenneth Moton. Reporter: Tonight, John Kelly's stunning parting words as chief of staff, telling the "L.A. Times" the white house has given up on president trump's signature campaign the southern border, saying, "To be honest, it's not a wall. The president still says wall. Often times frankly he'll say barrier, or fencing. Now he's tended toward steel slats." We're going to have tremendous border security, that will include the wall. Reporter: Kelly did say the president was right to make border security a top priority. "We do have an immigration problem." "If we don't fix the laws, then they will keep coming," he said. "They have known, and they do know, that if they can get here, they can, generally speaking, stay." General Kelly described his 18-month tenure as a "Bone crushing hard job." Once saying this in jest -- I did something wrong and god punished me, I guess. Reporter: Kelly recalled that trump would press advisers on the limits of presidential authority under the law. But added trump never ordered him to do anything illegal, "Because we wouldn't have," Kelly said. That check on the president, something fired secretary of state Rex tillerson recently spoke about. I'd have to say to him, well, Mr. President, I understand what you want to do but you can't do it that way. It violates the law. Reporter: Kelly saying his time at the white house "Is best measured by what the president did not do," claiming last year he talked the president out of withdrawing troops from Afghanistan. John Kelly will be leaving at the end of the year. Reporter: Shortly after trump confirmed Kelly's departure he announced half the 14,000 soldiers in Afghanistan, and all of those in Syria, would be leaving the battlefield. They're all coming back, and they're coming back now. Reporter: Kelly said he decided to leave this white house after the midterm election. Asked why he stayed a year and half during some very tumultuous months, Kelly simply said, duty. Jon? Kenneth, thank you. Meantime, with the clock

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