President Trump’s plan to continue deploying American military forces in Syria goes beyond his authority under federal law, according to a top Senate Democrat.

“We are on the precipice of committing U.S. forces to another forever war,” Maryland Sen. Ben Cardin, the ranking member on the Foreign Relations Committee, said Thursday.

That was a rebuke of Secretary of State Rex Tillerson, who outlined Trump’s policy for Syria following the destruction of the Islamic State as a landholding terrorist organization. Tillerson explained that U.S. forces and diplomats must work to prevent the resurgence of ISIS and the domination of Syria by Iranian-backed terrorists. But Cardin maintained the new policy exceeds anything authorized by Congress.

“I am extremely disappointed that the Trump administration announced a significant change in U.S. policy — the commitment of U.S. forces for an indefinite period of time in Syria — without first consulting Congress,” Cardin said. “The Trump administration lacks the authority to keep U.S. military forces in Syria after the defeat of ISIS.”

Trump, like former President Barack Obama, has traced the legal authority for counter-ISIS operations back to the legislation that authorized military action action against al Qaeda in response to the Sept. 11, 2001 terrorist attacks. ISIS formed out of the remnants of al Qaeda’s affiliate in Iraq. Tillerson tied the new Syria policy to that legal basis by noting the potential for ISIS to rehabilitate itself in the absence of U.S. forces.

“ISIS presently has one foot in the grave, and by maintaining an American military presence in Syria until the full and complete defeat of ISIS is achieved, it will soon have two,” he said.

In Tillerson’s telling, such a complete victory — over ISIS or Iranian forces in the country — depends on the success of a broader effort to bring peace and stability to Syria.

“Ungoverned spaces, especially in conflict zones, are breeding grounds for ISIS and other terrorist organizations,” he said. “U.S. disengagement from Syria would provide Iran the opportunity to further strengthen its position in Syria. As we have seen from Iran’s proxy wars and public announcements, Iran seeks dominance in the Middle East and the destruction of our ally, Israel. As a destabilized nation and one bordering Israel, Syria presents an opportunity that Iran is all too eager to exploit.”

The unveiling of the plan could renew congressional interest in crafting a new legislation defining the president’s legal authority to conduct counter-terrorism operations. For years, lawmakers in both parties have struggled to agree on the details of a new authorization of the use of military force.

“Congress has been unable to bridge the gap between those who see a new AUMF as primarily an opportunity to limit the president and those who believe constraining the commander in chief in wartime is unwise,” Senate Foreign Relations Chairman Bob Corker, R-Tenn., said during a recent hearing.

Tillerson’s announcement is sure to spark a new round of debate on the policy, though. “The State and Defense Departments must immediately consult with the members of the Senate Foreign Relations Committee, which retains jurisdiction over the use of military force,” Cardin said.