The open threat to jail a political opponent is unprecedented in U.S. political history.
Clinton repeated that she made a mistake using a private email server during her tenure at the State Department.
Earlier this year, the Department of Justice declined to press charges against Clinton for deleting emails three weeks after receiving a House subpoena. She says the emails were deleted because they were personal and private rather than work-related.
FBI Director James Comey testified that the investigation "didn't find any evidence of evil intent and intent to obstruct justice." An FBI investigation concluded that many of the deleted emails were, in fact, work-related.