The president's opinion, because it is his, is prima facie evidence for the opposite conclusion. It is, however, not sufficient evidence. Consider the debate between two serious people who have immersed themselves in the history of the Appointments Clause, which says:
"[The president] shall nominate, and by and with the advice and consent of the Senate, shall appoint ambassadors, other public ministers and consuls, judges of the Supreme Court, and all other officers of the United States, whose appointments are not herein otherwise provided for, and which shall be established by law: but the Congress may by law vest the appointment of such inferior officers, as they think proper, in the President alone, in the courts of law, or in the heads of departments."
The debate turns on the distinction the Supreme Court has drawn between "inferior" and "principal" officers. If Mueller is among the latter, his appointment was invalid because he was neither nominated by the president -- he was appointed by Deputy Attorney General Rod Rosenstein -- nor confirmed by the Senate. Steven G. Calabresi, professor at Northwestern University Law School and co-founder of the Federalist Society, argues as follows:
By "long-standing practice," Congress and the executive branch give principal-officer status to all "important and powerful" officials, even those who have a boss who can fire them. In 1976, the Supreme Court invalidated the law that created the Federal Election Commission to be composed of two members nominated by the president, two by the speaker of the House and two by the president pro tempore of the Senate.
The court held that all six must be nominated by the president as principal officers. Mueller, says Calabresi, is much more important and powerful than an FEC member. Congress has stipulated that the 93 U.S. attorneys are principal officers, and Mueller has, Calabresi says, "acted and has behaved like," and is "much more powerful than," any U.S. attorney.
Compare, for example, Mueller's job relative to that of the U.S. attorney for Wyoming. Mueller has "nationwide jurisdiction" and powers (e.g., to indict foreign citizens and corporations "without clearance from [the Justice Department]") that have had "a major effect on" U.S. foreign policy, powers that "in effect and in practice" are "akin to" those exercised by an assistant attorney general, a principal officer.
Mueller has been "without any real supervision" by Rosenstein, "who has treated Mueller as if he was 'independent.'"
Furthermore, Calabresi says Mueller cannot be an inferior officer because "Congress has not, by law vested in the attorney general, the power to appoint special counsels to investigate wrongdoing" by high officials. The Appointments Clause creates a "default rule" that all U.S. officers are principal officers and it takes an "affirmative action" -- a statute -- to empower the attorney general to appoint a special counsel as an inferior officer, which Congress has not passed.
The 1978 law that vested in a special court the power to appoint independent counsels expired in 1999.
Writing in vigorous rebuttal, George Conway, a New York lawyer (whose wife Kellyanne works for the president who hopes Calabresi is correct), argues that Calabresi incorrectly asserts that Mueller must be a principal officer because he does not have a supervising and directing boss. Conway says:
Rosenstein has testified to Congress that he is "exercising my oversight responsibilities" concerning Mueller, with whom he has "ongoing discussion," who "consults with me" about his investigation, and who has "received my permission" regarding the scope of the investigation. So Mueller, like an inferior officer, has "a boss" by whom he is "directed and supervised," and whose "orders" Mueller is "faithfully following." No presidential power has been diminished because Mueller's mission was defined by a regulation written within the supervising executive branch.
And although U.S. attorneys are principal officers, vacancies in the 93 offices can be filled for 120 days by the attorney general without Senate involvement and then "indefinitely" by district courts. Calabresi replies: 100 senators would have conniptions were U.S. attorneys treated as inferior officers not requiring senatorial consent.
Two intelligent lawyers disagree about this momentous matter, concerning which the Supreme Court's nine justices might eventually be dispositive. If Mueller's appointment is challenged, and the case gets to the court, and five justices reason as Calabresi does, Mueller's subpoenas, indictments and other acts will be null and void.