Executive Secrecy Keeping information secret from Congress Next: Press Freedoms

The Context

Presidents of both parties have claimed that executive privilege applies not only to their own internal White House communications, but also to internal deliberations within government department and agencies that do not involve the president. The Trump legal team has further argued that congressional subpoenas whose primary goal is to uncover potential wrongdoing, rather than to inform bill writing, are invalid because they lack a legitimate legislative purpose.

The Question

Does executive privilege extend to agency deliberations that did not involve the White House? Does Congress have legitimate constitutional authority to issue subpoenas compelling disclosure of information about potential wrongdoing?