Outgoing White House chief of staff John Kelly, reflecting on his tenure working with President Trump, blamed former Attorney General Jeff Sessions for the controversial "zero tolerance" policy that separated immigrant families at the southern border. In an exit interview with the Los Angeles Times, he also admitted the border wall — a signature promise by Mr. Trump — isn't really a wall.

"To be honest, it's not a wall," Kelly told the paper. "The president still says 'wall' — oftentimes frankly he'll say 'barrier' or 'fencing,' now he's tended toward steel slats. But we left a solid concrete wall early on in the administration, when we asked people what they needed and where they needed it."

Kelly will leave the administration on Wednesday and will be replaced by Mick Mulvaney as acting chief of staff. In his interview with the L.A. Times, Kelly reflected on the highs and lows of his tenure, laying the blame for the child separation policy at the feet of Sessions, who was fired after the midterm elections in November.

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In May, Sessions announced the Justice Department would pursue prosecution of anyone entering the country illegally, meaning adults traveling with children would be separated from their family members. Kelly said the announcement had caught the White House by surprise, even though Kelly himself had previously raised the possibility that separating families could serve as a deterrent for illegal immigration.

"What happened was Jeff Sessions, he was the one that instituted the zero-tolerance process on the border that resulted in both people being detained and the family separation," Kelly said. "He surprised us."

The administration backtracked in June, with Mr. Trump signing an executive order to keep families together even as the Justice Department pursues prosecutions.

Kelly said he was looking forward to taking a break from what he called a "bone-crushing hard job." Kelly served 46 years in the Marines and retired in January 2016 as the U.S. military's longest-serving general. As chief of staff, he said he typically woke up at 4 a.m. and came home at 9 p.m., where he kept working.

"I'm guarded by the Secret Service. I can't even go get a beer," he joked.