Secretary of State Rex Tillerson informed a senator in a recently-revealed letter that President Trump considers himself to possess inherent constitutional authority to launch military action without any act of Congress, a sweeping assertion that appears to resurrect from the early George W. Bush years the most imperial notions of the presidency.

Now a group comprised mostly of former Obama administration attorneys is suing to force disclosure of a seven-page Justice Department document they believe codifies the broad legal claim. As they await a judge’s verdict, they believe the secret opinion they seek provides a blueprint for the presidency to put the final nail in the long-constructed coffin for Congress’ own constitutional authority over American war.

Last April, Senator Tim Kaine watched Trump launch a cruise-missile fusillade against a Syrian airbase firmly under the control of regime dictator Bashar Assad. Trump publicly justified attacking the airbase as a means to impose costs on Assad for his chemical weapons attack.

Significantly, doing so bore no relationship to any congressionally-authorized war—not any adversary targetable under the 2001 Authorization to Use Military Force (AUMF)—nor any defense of the U.S., its allies or its articulable interests. Kaine wondered: what was the administration’s legal basis for striking the Shayrat airfield?

“ Many presidents have justified military force [with] an emergency need to defend U.S. forces or allies from actual attack. Secretary Tillerson has attempted to slip a punitive strike into that category of defense... [That] response violated international law and the U.S. Constitution. ” — Prof. Mary Ellen O'Connell

It took until October for Kaine to get an answer. Rex Tillerson, the secretary of state, provided a three-sentence explanation in writing for a hearing on the AUMF; The Daily Beast acquired it after Kaine referenced it in a letter to Tillerson last week. Tillerson pointed to an asserted constitutional authority.

“The April 6 U.S. missile strike on Shayrat airfield in Syria was not based on the authority of the statutory authorizations for use of military force that we have been discussing at this hearing,” Tillerson told Kaine.

“The President authorized that strike pursuant to his power under Article II of the Constitution as Commander in Chief and Chief Executive to use this sort of military force overseas to defend important U.S. national interests. The U.S. military action was directed against Syrian military targets directly connected to the April 4 chemical weapons attack in Idlib and was justified and legitimate as a measure to deter and prevent Syria’s illegal and unacceptable use of chemical weapons.”

Kaine wasn’t the only one interested in the legal wellspring of the Syria strike. A bipartisan group featuring several former Obama administration lawyers, the Protect Democracy Project, learned in court that Tillerson’s three-sentence answer heralded a more expansive one.

Shortly after the Shayrat strikes, the project filed a lawsuit under the Freedom of Information Act to compel disclosure of any internal legal analysis of the strikes the administration conducted. The suit has yet to result in disclosure. But it revealed the existence of a classified assessment from the Justice Department’s influential Office of Legal Counsel whose application looks to be broader than the Syria strike.

The document, according to Office of Legal Counsel attorney Paul Colborn, is the product of attorneys across multiple federal agencies “providing advice and recommendations to the president and/or other senior Executive Branch officials regarding the legal basis for potential military action.” The undated document was apparently written on or around April 6, the day of the Syria strike. A Justice Department official declined to comment or explain the document further.

Citing the filings, Kaine on Friday raised warnings in a follow-up letter to Tillerson, first reported by NBC, that the authorities the administration claimed risked an end-run around Congress to “become precedent for additional executive unitary action, including this week’s U.S. airstrikes in Syria against pro-Assad forces or even an extremely risky ‘bloody nose’ strike against North Korea.” Tillerson last month declared that U.S. troops will remain in Syria indefinitely, for missions beyond the anti-ISIS mission that itself has only a tenuous connection to the 2001 AUMF.

“President Trump has claimed an extreme view of the president’s Article II powers—for example, saying falsely that he has an ‘absolute right’ to do whatever he wants with the Justice Department,” said Justin Florence, Protect Democracy’s legal director and an attorney in Barack Obama’s White House counsel’s office.

“In the area of war powers, when prior administrations have relied on the president’s authority to conduct military activity they’ve released their legal opinions. It’s time for this administration to release the Syria war powers memo so that Congress and the public understand the full extent of the executive power claims.”

“ The consequences of the Trump Administration’s legal theories could extend beyond the April 2017 Syria strike to using force in North Korea or elsewhere in the world. ”

While it is not clear what the still-classified memo authorizes, the Trump administration is not the first in recent memory to assert broad warfighting mandates under its Article II authorities. In application, the previous Republican presidency asserted broad constitutional claims about not just the waging of war, but derivative activities, such as interrogation, detention and surveillance.

During George W. Bush’s first term, a coterie of attorneys, including OLC deputy chief John Yoo, relied extensively on Article II to provide the administration legal cover for activities it described as fundamentally entailed in warfighting, such as warrantless mass domestic surveillance and torture, in violation of federal laws. In aggregate, their claims, often called the Unitary Executive Theory, held that in times of war, the presidency’s constitutional powers are at a maximum, permitting a president to override Congress.

“This President’s claims of executive power have been expansive. Until we see the memo, we don’t know how far those claims go,” said Protect Democracy’s Florence. “The consequences of the Trump Administration’s legal theories could extend beyond the April 2017 Syria strike to using force in North Korea or elsewhere in the world, and could have implications for other government activities as well.”

There are already signs that the Trump administration’s view of its inherent constitutional powers during wartime extends beyond warfare to subsidiary, entailed activities. A recent Justice Department court filing showed that the government is relying in part on Trump’s claimed Article II powers to indefinitely detain a U.S. citizen captured five months ago in Syria on suspicion of working for the Islamic State.

In addition to two early-2000s congressional authorizations that legal experts consider dubiously applicable to ISIS, the Justice Department contended in the filing, “the Executive Branch also has inherent authority to direct the deployment of military forces and, as part of that authority, the power to detain combatants captured on the battlefield for as long as U.S. troops are engaged in active hostilities on that battlefield.”

But to the University of Notre Dame’s Mary Ellen O’Connell, Tillerson’s assertion—and whatever the Office of Legal Counsel has written in secret—papers over an illegal strike on Syria, and potentially augurs more.

“Many presidents have justified military force without Congressional action in the face of an emergency need to defend U.S. forces or allies from actual attack. Secretary Tillerson has attempted to slip a punitive strike into that category of defense. The chemical attacks on Syrians were by Syrians. The U.S. punitive response violated international law and the U.S. Constitution,” said O’Connell, an international law expert.