There was a time when it looked like Attorney General Jeff Sessions was faithfully trying to keep the Department of Justice free of the impetuous will of the president. By recusing himself from handling matters related to the 2016 campaign, including the Russia inquiry that eventually morphed into Robert Mueller’s special counsel probe, he had helped sustain the legitimacy of his office and of rule under law in this country.

But Sessions’ latest act—of unceremoniously firing career FBI officer Andrew McCabe right before he would have been entitled to his pension—undermines the independence of his office and makes him look as if he is under the thumb of the president who has threatened Sessions’ job as well. Trump spent much of the weekend triumphantly tweeting that McCabe’s integrity had been diminished before going after Mueller by name for the first time. If Sessions’ action were done to protect President Trump rather than to promote the public interest, McCabe’s firing would be invalid because of an overlooked requirement of our Constitution and of his office. The Constitution may ultimately protect Mueller from being fired, as well.

At some basic level, our constitutional scheme bakes in the attorney general’s cowardice. Since the attorney general is constitutionally removable at will, he can’t help but think about what his boss wants done.

And yet there is another legal command on the AG that is rarely appreciated: officers of the federal government are bound by oath. Here is the text of the oath (italics added) that Sessions had to take:

I, Jeff Sessions, do solemnly swear (or affirm) that I will support and defend the Constitution of the United States against all enemies, foreign and domestic; that I will bear true faith and allegiance to the same; that I take this obligation freely, without any mental reservation or purpose of evasion; and that I will well and faithfully discharge the duties of the office on which I am about to enter. So help me God.

The source of these duties is not merely the oath, either. Sessions’ solemn promise reflects a deeper constitutional commitment: to pursue only the public interest, not private interests. The Constitution commands the president to “take care that the laws be faithfully executed” and to take a specific oath “to faithfully execute” the office. As we’ve described in the Washington Post, the Framers drew the phrase “faithfully execute” from fiduciary instruments (like trusts) and colonial charters, which imposed duties of loyalty, care, good faith, and integrity against self-dealing and corruption. Trump is obligated to follow the same duties and take care that his administration does, too. The clause (“take care that the laws be faithfully executed”) means a president’s delegates inherit those same duties. So when the president delegates executive power to his Cabinet members, that delegation means that the Cabinet officials have legal duties of faith and faithfulness to pursue the public interest rather than the narrow self-interest of their boss.

The highest members of Trump’s Cabinet are constrained by this system of fiduciary government that scholars on the left and right agree was contemplated by the Framers. That is why there is so much language about “trust” and “faith” in the document itself. Public officials have the same obligations that the common law imposed on private fiduciary managers and directors, who could not and cannot orient their work to help themselves but are obligated to pursue the welfare of the collective enterprise.

Further, the DOJ has regulations that allow only the attorney general—or an official acting in that capacity—to dismiss a special counsel, but only for “misconduct, dereliction of duty, incapacity, conflict of interest, or for other good cause, including violation of Departmental policies.” Then the person responsible for the decision in the Department of Justice “shall inform the Special Counsel in writing of the specific reason for his or her removal.” These regulations also reflect fiduciary duties to act only for the right kinds of reasons and to be transparent about those reasons. Fiduciary principles would deny Trump and Sessions—or Deputy Attorney General Rod Rosenstein, who oversees the Mueller investigation due to Sessions’ recusal—the authority to unilaterally rescind or ignore those rules to engage in self-dealing or self-protection.

It is this kind of constitutional faith and this seriousness about the office that led former attorneys general to resign in protest rather than fire other officers in the executive branch at the behest of the president. Attorney General Elliot Richardson and Deputy Attorney General William Ruckelshaus famously refused President Nixon when he asked them to fire a wholly professional executive branch official that Nixon felt threatened him personally. Today, we call this affair the “Saturday Night Massacre”—but one might see it with a different valence: The heads of the DOJ were willing to abide by the faith their oaths—and by delegation, the Constitution—required of them, even if it meant their own removal.

This constitutional theory is deeply grounded in the history of Anglo-American common law and public law.

We can only hope Sessions re-engages his faith. After all, a few short weeks after Richardson and Ruckelshaus showed where their true allegiances were—to the rule of law rather than to a boss looking to put his private interest above the public interest—the people really began supporting impeachment and Nixon resigned. This was a political question at the time and it could remain so. But if Mueller is ultimately fired by Sessions or someone else at the behest of Trump, it could ultimately become a legal question as well.

American courts have given the language of “faithful execution” in the context of public officials enforceable meaning in past precedents, binding public officials to good faith and loyalty. For example, one case in federal court has held poultry inspectors at the Department of Agriculture to have enforceable public fiduciary obligations to the United States; another has held a former CIA agent to a fiduciary duty of confidentiality. It could be possible for Mueller to seek an injunction from a federal court based on these arguments to block his firing from any official acting for self-protection against the public interest.

On the one hand, it may seem like such an injunction would be an unprecedented effort based on a novel constitutional theory. On the other hand, there are federal precedents for applying fiduciary rules to public officials, and this constitutional theory is deeply grounded in the history of Anglo-American common law and public law. Our founders relied on this tradition to protect the public interest.

The Framers worried about executive abuse of power and designed a fiduciary Constitution of checks and balances to ensure safeguards against that form of corruption. They might not have foreseen Russian bots on Facebook and Twitter, but they foresaw a risk of tyranny and executive overreach, and they included the language of faith and trust to empower an independent judiciary to preserve their republican government.