Kellyanne Conway's husband just explained on Twitter that Congress CAN subpoena the interpreter

[onenote]

9. Conway's legal analysis is overly simplistic

The fact that Putin was a party to the conversation does not mean that it isn’t privileged.

From the Supreme Court decision in the Nixon case: “The President's need for complete candor and objectivity from advisers calls for great deference from the courts. However, when the privilege depends solely on the broad, undifferentiated claim of public interest in the confidentiality of such conversations, a confrontation with other values arises. Absent a claim of need to protect military, diplomatic, or sensitive national security secrets, we find it difficult to accept the argument that even the very important interest in confidentiality of Presidential communications is significantly diminished by production of such material for in camera inspection with all the protection that a district court will be obliged to provide.”

Trump would claim and the courts might agree that the conversation between trump and Putin must remain confidential to protect military diplomatic or national security secrets. I don’t know how the courts would rule but it’s not the slam dunk Conway’s tweet suggests.