You should have read a little further...
Following a contempt citation, the presiding officer of the chamber is instructed to refer the matter to the U.S. Attorney for the District of Columbia;[14] according to the law it is the "duty" of the U.S. Attorney to refer the matter to a grand jury for action. However, while the law places the duty on the U.S. Attorney to impanel a grand jury for action, some proponents of the unitary executive theory argue that the Congress cannot properly compel the U.S. Attorney to take this action against the Executive Branch, asserting that the U.S. Attorney is a member of the Executive Branch who ultimately reports only to the President and that compelling the U.S. Attorney amounts to compelling the President himself[citation needed]. They argue that to allow Congress to force the President to take action against a subordinate following his directives would be a violation of the separation of powers and infringe on the power of the Executive branch. The legal basis for this position, they contend, can be found in Federalist 49, in which James Madison wrote “The several departments being perfectly co-ordinate by the terms of their common commission, none of them, it is evident, can pretend to an exclusive or superior right of settling the boundaries between their respective powers.” This approach to government is commonly known as "departmentalism” or “coordinate construction”.
