The recent saber rattling against Iran raises the question of whether the president can take the country to war on his own. Unfortunately, much of the legal advice that presidents have received on war powers remains in a veritable lock box in the Justice Department Office of Legal Counsel. When questions arise about what the government has the power to do, such as whether unilateral action is lawful, it is often the Office of Legal Counsel, not a court of law, that sets the scope of executive power. It builds on its own precedent over time, creating a form of law within the executive branch. But many Office of Legal Counsel opinions remain secret decades after the fact. Because of this, a body of secret law has become a building block of contemporary presidential power.

This system of secrecy curtails the ability of historians like me to research some of the most consequential opinions justifying executive actions. It also undermines the transparency the public is entitled to. That is why I joined four other scholars, along with the Campaign for Accountability and the Knight First Amendment Institute, in a legal challenge aimed at making public the secret law that informs presidential decisions.

An example of the way one presidential action builds upon another and why the history of this secret law matters is a published Office of Legal Counsel opinion from 2014 which found that President Obama had legal authority to order targeted airstrikes without authorization from Congress against the Islamic State of Iraq and the Levant. It relied, in part, on the American invasion of the Caribbean island nation of Grenada in 1983 under President Reagan. This and other executive actions showed that presidents regularly used force without involving Congress. But what, if anything, did the Office of Legal Counsel say to Reagan at the time of the invasion about whether it was lawful? We do not know.

What we do know is that Reagan justified the invasion of Grenada on expansive grounds. When American forces invaded the island in October 1983, it came as a surprise not only to Grenadians, but also to the American people, most of whom had never heard of the country. The objective for Reagan was to oust a Soviet aligned government near American shores. He did not ask Congress to authorize this action and did not notify them in advance. Instead, he cast it as a rescue operation, requiring secrecy. A military coup had just seized power in Grenada, and hundreds of American medical students attended school there. In spite of military mishaps, American forces overwhelmed Grenadian and Cuban forces on the island. The operation left American military casualties with 18 dead and 116 injured. Civilians on the island were also killed.

Reagan notified Congress pursuant to the War Powers Resolution after the fact. He explained in a speech to the nation that the invasion was justified due to the presence of Americans in Grenada during a period of unrest. The country had a duty “to go to the aid of its citizens if their right to life and liberty is threatened.” He said that he was also responding to an intervention request from the Organization of Eastern Caribbean States.

If the president has the power to send American troops anywhere in the world whenever American citizens are potentially in danger, that power is exceedingly broad. Moreover, the fact that neighboring states requested assistance should not diminish the war powers of Congress. Did the Office of Legal Counsel advise Reagan that the presence of American medical students, and the appeal from the Organization of Eastern Caribbean States, gave him power to send 2,000 troops to Grenada without seeking authorization from Congress? If so, were the arguments convincing, and should future presidents rely on them, as Obama did more than 30 years later? Because most Office of Legal Counsel opinions from 1983 remain under wraps, we do not have answers to these questions.

Opinions on the use of force are just a subset of what the Office of Legal Counsel is withholding from public release. Over the years, the Office of Legal Counsel has produced a large array of opinions on topics ranging from the role of the executive branch in shaping immigration law and policy, to authorizing covert operations and state surveillance, to pushing for criminal justice reforms or failing to address various civil rights concerns, including workplace and housing discrimination.

This enormous body of secret law undermines the ability of historians to examine the past, and it hampers policymakers seeking to draw lessons for the future. Democracy requires transparency, and transparency requires, at least, that decades old Office of Legal Counsel opinions that remain a building block of presidential power be released to the public.