“Is it your position that whether the president has properly reported his finances [under federal disclosure laws], that’s not subject to investigation by Congress?” Mehta asked.

“Say a president was involved in some corrupt enterprise — you mean to tell me because he is the president of the United States, Congress would not have power to investigate?” Mehta asked, saying that what if “we’re talking about a presidential violation of a constitutional prohibition that only Congress has authority to approve,” such as the acceptance for emoluments or gifts from a foreign government.

[William S.] Consovoy answered yes, saying that determining whether a president properly disclosed his finances was a “pure law enforcement function,” not a matter for Congress, whose fundamental duty, he said, is writing bills.

And if Congress did seek to enact legislation, whether to tighten ethics requirements, fight public corruption or enforce a constitutional prohibition on acceptance of foreign emoluments, Consovoy said, “I don’t think there is any permutation of any of these proposals that could pass constitutional muster,” because they would interfere with the president’s execution of his duties, or add qualifications for his office.