Josh Blackman, in three successive postings for Lawfare, and co-commentators David Rivkin and Lee Casey in a separate piece for the Wall Street Journal, have been developing the case that a president firing an FBI director or other senior law enforcement official may not subject to impeachment for obstruction of justice. Their approaches are somewhat different: Blackman is working out a more fully developed, nuanced theory of how we should see a conflict between congressional impeachment power and claims of executive authority. But these authors have all offered support for the proposition that, however corrupt or (as Rivkin and Casey put it) “nefarious” a president’s motive may be, his constitutional authority necessarily includes removing from office those officials who presumptively answer to him. Congress, they say, must stand down.

Rivkin and Casey seem to distinguish between Congress “criminalizing” obstruction and impeaching him for the same actions, but their stout defense of the president’s firing of James Comey or Robert Mueller “for any reason, good or bad” raises the obvious question: On what grounds, then, does Congress impeach a president for acting clearly within his constitutional authority? If by holding the president accountable at law for obstruction, we risk the establishment of “legislative supremacy—a result the Framers particularly feared,” how does Rivlin and Casey’s concern with the separation of powers not also apply to Congress’ use of the impeachment power to oust a president for the same offense? Blackman asserts in explicit terms that the president’s executive powers “curtail the scope of the conduct [such as firing Comey] that qualifies as a ‘high Crime.’”

It is not too early to confront and examine closely this line of argument. Allies of the president have escalated their attacks on the special counsel, and Trump has expressed his own unhappiness with both the fact and course of the Russia investigation. He has denied that he will fire Mr. Mueller, but if his discontent rises and he fires the special counsel, the immediate next question will be: how will—and may—Congress respond?

Some Republican members of Congress who once staunchly defended the Mueller investigation now appear to be taking a step back. A firing will require them and others in their ranks to settle on a position. Some may on an attack on the Mueller investigation’s impartiality rely for their defense of the president. But others, looking for higher ground, may be drawn to a constitutional defense and find it in a claim that the president had every right to fire this or any other of his subordinates. They may argue that their hands are tied: Whatever concerns they may have about the president’s conduct, impeachment is not a course that is constitutionally available to them.

I have questioned why, in this view, the issue of presidential motive is irrelevant and what it means for the Congress, in the discharge of its impeachment power, if the president can disable the prosecutorial machinery for looking into this question of criminal obstructive intent. By firing Comey, and perhaps soon Mueller, Trump may in one blow undermine the independent administration of the criminal laws and impair Congress’s capacity for determining the existence of unlawful motive.

There is a still another problem with the argument that the president’s executive power to remove an official prevails over Congress’ power to impeach. It overstates the constitutional breadth of the executive authority that the president may assert in defending against impeachment relating to the firing of officials. In doing so, it misses the momentous importance to the scheme of separated powers of upholding Congress’ authority to impeach a president for obstructive intervention in criminal law enforcement. We should worry about executive, not legislative, supremacy if Congress cannot act to hold the president to account for these actions. Future presidencies will have devastating new ammunition they may use to subdue, control or intimidate the legislature through the misuse of the Department of Justice for political or self-interested purposes.

Blackman cites the 1926 case of Myers v. United States for the proposition that there are limits to congressional impeachment authority where the president acts to remove a subordinate official. He puts some stock in the Myers majority’s questioning of the constitutional basis for Congress’ impeachment of Andrew Johnson for flouting the Tenure of Office Act. Of course, the dissents by Justices Louis Brandeis and Oliver Wendell Holmes do not embrace the majority’s constitutional perspective on that episode.

Moreover, Myers has limited significance in light of later case law on the reach of executive removal authority. It does only so much to strengthen the constitutional hand that Blackman seems to suggest that the president can play in a clash with the Congress over their respective constitutional authorities. The court’s treatment of presidential removal issues since Myers has veered back and forth between the more formalist position favoring the executive and a more functional one producing different results. The court has tended to look practically behind the sweeping assertions of executive power in particular contexts and in the discharge of specific functions, and it has sought to balance the actual costs to presidential control against other considerations.

On the specific question of executive management of the criminal justice process, the court in Morrison v. Olson affirmed the extensive limits on this authority that Congress built into the structure of the independent counsel statute. On a series of questions, including the Special Division’s power to terminate an investigation, eight of the nine justices went out of their way to find that the statutory design was consistent with Article III and to conclude that it did not run afoul of the take care clause or separation of power principles “taken as a whole.” The court did not accept the characterization of the independent counsel’s role as “purely executive.” Tellingly, the majority made a point of putting Myers in its place: The Court’s opinion included a terse footnote stating that “the only issue actually decided in Myers was that ‘the President had power to remove a postmaster of the first class, without the advice and consent of the Senate as required by the Congress.’”

So executive power in the context of criminal law enforcement is not all-or-nothing. The president can be afforded what the Morrison court term “sufficient” oversight and management responsibility without ceding him unfettered control with no regard to motive or consequence. To the extent that founding notions of presidential power count in this debate, it may help to note that, as Peter Shane has written, it is even “extremely unlikely” that “the founding generation conceptualized criminal prosecution as an inherently executive function.”

The result in Morrison may be explained in various ways, but certainly it is an example of how the court’s judgments on the core constitutional issues may be shaped by its sensitivity to vitally important background norms. In a case decided 8-1, the court was concerned to preserve a meaningful degree of independence from conflict of interest or outright abuse for federal criminal law enforcement—a norm of direct significance for the debate about this president’s ostensibly unqualified, unreviewable right to fire a Comey or a Mueller.

This norm lies behind policies common to all administrations, such as those governing permissible contacts between the Department of Justice and the White House. It is the basis for the expectation that nominees for attorneys general will assure Congress, as they routinely do, of their commitment to a department that is, in critical respects, sufficiently “independent.”

In the George W. Bush administration, the concern embodied in this norm provoked a clash between the president and the Congress over allegations of illicit political considerations in the termination of U.S. attorneys. As Peter Strauss wrote at the time: “All agree that there is no legal requirement to assert ‘cause’ for these removals; yet, in the view of many, the suggestion of inappropriately political control of prosecutions made these removals highly corrosive of rule-of-law considerations.”

At the most fundamental level of expression, the norm is woven out of this “rule of law” material. It simply reflects a belief that if the president is not “above the law,” he should not, for all practical purposes, be able to put himself there by manipulating the machinery of criminal justice.

But no less important is how the norm comports most closely with separation-of-powers concerns “taken as a whole.” If a president can interfere directly in the choice and course of criminal prosecutions, then standing on “pure” executive authority, he will have available a powerful tool for the dangerous aggrandizement of his office at the expense of the legislative branch. Just as he would be able to protect himself and his personal and political associates from liability for corrupt acts, he could wield the law against his political adversaries and use it to exact pliant behavior from the Congress. He can do this by ordering actions to be taken and by removing those officials who resist his orders.

An argument like the ones now appearing—that regardless of motive, a president dismissing senior law enforcement officials cannot commit obstruction for which he may prosecuted or impeached—invites presidential abuse of power and a dangerous imbalance in the relationship of the co-equal branches. It is hard to imagine a more compelling case for congressional response through impeachment. Congress would lack a sound basis for accepting the president’s argument that he cannot be impeached for the “executive” act of serially firing senior law enforcement personnel in an investigation that directly affects him, family members and political associates.

Depending on the course of events, this argument could come before the courts. It is conceivable that this president would attempt to challenge Congress’ authority to impeach him on these grounds. If he does, it would not be on terms helpful to his cause.

Mr. Trump would have to press his case as an executive who has repeatedly assailed his Department of Justice for investigating matters that the intelligence community and the Congress agree require urgent attention—Russian interference to destabilize the electoral process and sway a presidential election in Trump’s favor. Trump fired the FBI director for the director’s part in this inquiry, and few believe that the president has ruled out dismissing the special counsel. He has made clear his rage at the attorney general for following the recusal rules and staying out of this investigation—and only a sharp warning from congressional Republicans stopped him from also sending this cabinet officer packing. Trump has scorned the same official for failing to bring a prosecution against his opponent in the last election. What’s more, this president has also hinted at the use of the pardon power to stymie the Russia investigation, having already and early in his term employed it to spare a political ally the consequences of criminal contempt of court.

In spite of all this, the president might forge ahead with a claim that, in the exercise of his executive authority and as a matter of constitutional law, he is free to take these actions without accountability to the Congress in an impeachment proceeding. Should Mr. Trump direct his legal team to make this case, the result will be the one that he apparently hates above all others: losing.