Michael Flynn, former national security adviser to President Donald Trump, leaves following his plea hearing at the Prettyman Federal Courthouse in Washington, D.C., on Dec. 1, 2017. Sentencing documents indicate he has been helpful to the ongoing special counsel investigation.

Michael Flynn, former national security adviser to President Donald Trump, leaves following his plea hearing at the Prettyman Federal Courthouse in Washington, D.C., on Dec. 1, 2017. Sentencing documents indicate he has been helpful to the ongoing special counsel investigation.