Let the maggot "testify" but he/she/it should not be allowed to "plea bargain" or be given immunity. This maggot needs to be sent to prison for committing treason against the United States.
Unless this person is an elected congresscritter, they have committed a felony and there is no doubt they go directly to prison, or to the firing squad in time of war. There are mechanisms for disclosing illegal activity as a whistle blower and IT AIN'T RUNNING TO THE MSM.