This is all BS. We are talking about the President of The United States and an effort to remove him ether justifiably or trough some kind of deep state conspiracy. We have a right to know. The need to protect the identity of some source is heavily outweighed by the enormity of what they are trying to do. We absolutely have a right and a need to know.
It also occurs to me that they’re gearing up to use this story about protecting confidential sources as an excuse to drop a bunch of the criminal charges that Mueller has filed. In a criminal case, the defendant has a right to know who this person is and call him as a witness.
Why not now ? He is using "the process"
Why that ? To learn and to make others squirm.
When then ? Some in 2018; and some more in 2020.