Answer
The U.S. president during Otto Warmbier's imprisonment in North Korea from 2016 until his release in 2017 was Barack Obama. Warmbier, an American student, was arrested in January 2016 while visiting North Korea and was sentenced to 15 years hard labor for attempting to steal a political propaganda poster. He was released in June 2017 in a comatose state and died shortly after returning to the United States.