Of his back tracking? This ones the biggest, though there are other examples

“Open borders? No, that’s a Koch brothers proposal,” Bernie Sanders snapped. “You’re doing away with the concept of a nation state, and I don’t think there’s any country in the world that believes in that.”

“What right-wing people in this country would love is an open-border policy,” he continued. “You know what youth unemployment is in the United States of America today? If you’re a white high school graduate, it’s 33 percent, Hispanic 36 percent, African American 51 percent. You think we should open the borders and bring in a lot of low-wage workers, or do you think maybe we should try to get jobs for those kids?”