John Kelly broke with the Trump administration’s immigration policies in his harshest criticism of the president to date.

Addressing Duke University on Wednesday, the former White House chief of staff called a wall along the entirety of the U.S.-Mexico border “a waste of money.”

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“We don’t need a wall from sea to shining sea,” said Kelly when speaking about Trump’s decision to declare a national emergency to secure border funding.

The former aide also came out against President Donald Trump’s decision to deploy National Guard troops to the border last fall—saying he “would always look for another way to do it”—while singling out Jeff Sessions for the White House’s controversial “zero tolerance” policy.

“The big separation of families, that was a decision made by the Attorney General,” said Kelly. “It kind of surprised us. It certainly caught DHS flat-footed and HHS, Health and Human Services, flat-footed.”

Despite Trump’s repeated portrayal of immigrants as dangerous lawbreakers, Kelly said most asylum seekers are “overwhelmingly not criminals” and are “people coming up here for economic purposes.”

The president’s former chief of staff also emphasized the importance of NATO—an alliance Trump has regularly questioned and challenged in public forums.

On advice for his successor, Mick Mulvaney, Kelly said he offered a parting piece of wisdom.

“Run for it,” said the former White House aide to laughter from the audience.