Donald Trump has a problem. Special counsel Robert Mueller is determined to interview him and has reportedly threatened to issue a grand jury subpoena if Trump refuses.

The most dangerous questions Trump faces concern exercises of the powers of his office, including allegedly: (i) firing FBI Director James Comey in an effort to end a law enforcement investigation; (ii) demanding the dismissal of Mueller; and (iii) dangling the prospect of pardons to tamper with witnesses, as the special counsel’s questions suggest Trump may have done with Michael Flynn.

Being truthful about such matters could require Trump to admit engaging in crimes. Lying is also a bad option, given the likelihood there’s evidence to counter any falsehoods. Asserting the Fifth Amendment could put an end to Trump’s political viability.

Trump partisans suggest he should assert complete immunity to a criminal investigatory subpoena. That gambit is bound to fail. As Bob Bauer demonstrated in Slate, it is at odds with at least two Supreme Court precedents.

United States v. Nixon addressed President Nixon’s refusal to comply with a subpoena for the White House tapes. Nixon claimed the subpoena invaded executive privilege, which permits the shielding of presidential communications from intrusion. The court agreed the president enjoys a constitutional “protection of confidentiality” but said that protection is not absolute. It must yield to “the duty of the Judicial Branch to do justice in criminal prosecutions.” The court ordered Nixon to release the tapes.

In Clinton v. Jones, President Clinton was ordered to comply with a subpoena for his testimony in a defamation lawsuit, despite the lesser import of civil proceedings.

Together, these decisions make it all but impossible for presidents to categorically defy subpoenas for testimony in criminal investigations. Ken Starr went so far as suggesting that Clinton could be impeached for asserting the executive privilege in response to a grand jury subpoena, because Clinton’s privilege claim was frivolous.

Trump therefore needs a new argument. The audacity of his alleged obstruction may hold the key. Only the president can fire any executive branch official or grant pardons for federal crimes. It is these unique presidential powers Trump may have used to frustrate criminal inquiries.

One other president has tried this: Nixon, who fired Special Prosecutor Archibald Cox after Cox subpoenaed the tapes. Nixon backed down and replaced Cox with Leon Jaworski, leaving the legality of the firing unaddressed.

In a recent press briefing, Sarah Huckabee Sanders asserted that President Trump “doesn’t have to justify his decision” to fire Comey. Trump counsel Rudolph Giuliani has likewise contended there’s “no evidence of obstruction of justice,” because “everything the president did, he has perfect authority to do” under the Constitution. Attorney Joe diGenova—who Trump briefly brought on to his legal team in March—asserted in an interview with Sean Hannity that the president had “ultimate authority to fire James Comey,” and that “Mueller cannot ask [Trump] about that.”

As these statements indicate, Trump seems poised to force the issue Nixon left on the table by contending the president has an absolute right under the Constitution to fire (as well as to pardon) any official, regardless of purpose.

If the claim that Trump is immune from criminal liability for firing or pardoning is accepted by the courts, then the president could well avoid having to testify before a grand jury about the same matters by asserting executive privilege. The Nixon decision compelling presidential compliance with a subpoena was based on the need to investigate potential crimes. If a president’s firings and pardons can never be mechanisms for crimes, the criminal investigation exception to the executive privilege may be inapplicable to such matters.

Thus, by pressing his authority to the limit, Trump might break new legal ground.

Unlike Nixon, Clinton did not try to fire the man leading the investigation into his actions; in fact, he couldn’t fire Ken Starr. Under the then-operative independent counsel law, the authority to hire and fire independent counsels resided in a court.

That law has since expired. But issues surrounding it lie at the heart of the arguments regarding executive power that Trump is likely to make in challenging a Mueller subpoena.

In Morrison v. Olson, the Supreme Court upheld the independent counsel law over the lone dissent of Justice Antonin Scalia. Scalia argued that criminal investigations and prosecutions are “quintessentially executive function[s]” and can’t be delegated to other branches.

For many advocates of executive power, Scalia’s dissent is a template for the so-called unitary executive doctrine, which posits the president is constitutionally entitled to have full, and largely unpoliced, control of the central functions of the executive branch.

Jed Shugerman convincingly argues against modeling future Supreme Court jurisprudence on Scalia’s expansive theory of executive power, including because it overstates the historical scope of presidential authority. Several current members of the Supreme Court, however, have demonstrated a proclivity for endorsing many of Scalia’s constitutional theories, including his expansive views of presidential authority. Consider that a majority of the Supreme Court may well be poised to uphold Trump’s travel ban, despite evidence the ban was the product of invidious and discriminatory presidential motives.

There is therefore reason to anticipate that some Supreme Court justices will take seriously an argument that the president’s exercise of the constitutionally delegated authority to fire executive branch officers and to pardon witnesses can’t be limited.

The argument has some surface appeal. The Supreme Court has long recognized that the Constitution defines certain areas of broad executive powers. Certain of those powers were derived from authority previously held by the king, including the pardon power.

Yet as stated in Nixon:

In designing the structure of our Government and dividing and allocating the sovereign power among three co-equal branches, the Framers of the Constitution sought to provide a comprehensive system, but the separate powers were not intended to operate with absolute independence.

If the president can fire law enforcement officers to free himself of criminal peril, it could license the very kind of outright corruption that led the colonists to revolt against the British crown, and allow the presidency to become a mechanism for tyranny.

This rule could render criminal laws enacted by Congress virtual nullities and also undermine the power of courts to do justice, in matters touching on the president’s compliance with the criminal laws.

As during the summer of 1974, when United States v. Nixon was decided, this summer may witness a judicial battle over whether the president has the power to manipulate the criminal investigatory process in his favor.

Warren Burger, an appointee and friend of Nixon, authored the Nixon court’s unanimous opinion rejecting that president’s gambit. Hopefully, the Supreme Court will rebuff any similar Trump effort to frustrate the nation’s justice system.