Former White House chief strategist Stephen K. Bannon says that the biggest mistake the Trump campaign made after winning the election was trusting the establishment to staff the populist president-elect’s administration.

“In the 48 hours after we won … you might call it the original sin of the administration. We embraced the establishment,” Bannon said during an interview with CBS News anchor Charlie Rose for 60 Minutes. “I mean, we totally embraced the establishment.”

He explained that he and Trump, his son-in-law Jared Kushner, and the rest of the family realized that they had to put together a government and let establishment Republicans into the administration.

“Our whole campaign was a little bit the island of misfit toys,” Bannon said.

He said that Senate Majority Mitch McConnell did not want Trump to drain the swamp and was acting against the president’s populist, economic agenda.

“They do not support the President’s program. It’s an open secret on Capitol Hill. Everybody in this city knows it,” he said.

Bannon’s 60 Minutes interview — his first since leaving the White House and returning as executive chairman of Breitbart News in August — aired Sunday night on CBS.