One of the greatest powers that can be granted to a national chief executive is jurisdiction over law enforcement. From the French President’s authority over the Ministry of Justice to the American President’s authority over the Department of Justice (DOJ), a number of states entrust their chief executive with significant control over the nation’s top law enforcement bodies. While these oversight powers are often exercised to achieve legitimate aims, problems arise when an executive uses his authority to shield himself or his associates from legal accountability. Such misuse of the chief executive’s authority over law enforcement is itself corrupt—an abuse of the president or prime minister’s public power to protect his private interests—and can foster the culture of impunity that allows other forms of corruption to thrive. But policing this sort of improper interference is challenging.

One possible limit on corrupt presidential interference with law enforcement is the fact that such interference may itself be a crime. In the United States, for example, it is a felony—known as “obstruction of justice”—for a government official to “corruptly” use the power of his or her office to “obstruct” a “pending or contemplated official proceeding” (such as a trial or investigation). But as Special Counsel Robert Mueller’s investigation into former President Donald Trump made clear, the current version of the obstruction of justice statute may be inadequate to check this form of presidential corruption.

For starters, it’s not clear whether the obstruction of justice statute, as currently written, even applies to a sitting president. (Scholars have disagreed on this point, with some arguing that the current statute does not apply to the president—see here and here—and others arguing to the contrary that it does.) That problem, though, has an easy fix: As Bob Bauer and Jack Goldsmith’s recent book has argued, Congress can and should amend the statute to state explicitly that a sitting president can commit obstruction of justice. Another difficulty is that, as Robert Mueller’s report stressed, under current DOJ policy, a sitting president cannot be criminally indicted. This too could be changed. The deeper and harder problem is that because in the U.S. system the president may legitimately seek to influence the conduct of criminal investigations, and because the president’s motives may be ambiguous or mixed, it is very hard, perhaps impossible, to prove that the president’s actions with respect to a pending or contemplated official proceedings were “corrupt.” Take President Trump’s decision to fire FBI Director James Comey. The Mueller Report concludes that President Trump fired Director Comey to save his presidency (which seems like a corrupt motive). Yet some claim that President Trump also had other, more legitimate reasons for firing Director Comey, including concerns about partisan bias in Comey’s investigations. And even if one contests that claim in this particular case, it’s not hard to imagine a situation in which a President moved to impede an investigation that both threatened the president’s personal interests and that the President thought was unwise or improper.

How should the law treat such cases, if the goal is to ensure that a U.S. President is not above the law, while simultaneously giving the President appropriate latitude oversee federal law enforcement?