In the letter, he said that the documents McGahn has belong to the White House, not McGahn.
This gives the White House effective control over whether McGahn complies going forward.
So that brings us to a broader question—Can the White House block the document request or his testimony?
Even if this isn’t technically a waiver—the White House will argue it wasn’t—it destroys any confidentiality argument they have.
But the alternative (a lawsuit) could take a long time unless the court greatly expedited the process.
It is also very hard to see how the Administration could block McGahn from testifying.
The problem, as I discussed in the column I linked above, is that without the documents it will be hard for Democrats to question McGahn well.
The upcoming battle, both legal and political, is as high stakes as it gets. Our Constitutional order is at stake. /end