Russia has invaded Ukraine. In response, President Biden has promised that the U.S. will impose "severe sanctions" against Russia for its actions.

But what are sanctions exactly? How do they work? Do they have a history of working? Do they work well?

Bruce Jentleson is a former State Department official. He has held numerous senior foreign policy positions in past U.S. administrations. He's a professor at the Sanford School of Public Policy at Duke University, and his new book is called Sanctions: What Everyone Needs to Know.

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