Here’s an unsettling prospect: British officials warn that a conflict between the United States and Iran could break out “by accident.” British Foreign Secretary Jeremy Hunt explained this week, “We are very worried about the risk of a conflict happening by accident, with an escalation that is unintended really on either side but ends with some kind of conflict.” Hunt argues that “a period of calm” is required to avoid war.

The United States Congress has the power to create such a period. As Senator Bernie Sanders says, “The United States Congress must do everything it can to prevent the Trump Administration’s attempts to put us on the brink of a catastrophic and unconstitutional war with Iran.” Specifically, argues Congressional Progressive Caucus co-chair Mark Pocan (D-WI), “Congress should demand that President Trump seek approval from the House and Senate before taking offensive action against Iran.”

That’s a simple demand and it should be made immediately. While the president says that he isn’t planning to start a war with Iran, his administration is sending ominous signals. The headlines tell the story: “US sends Patriot missile system to Middle East amid Iran tensions,” reports the BBC; “U.S. B-52 bombers reach Middle East in message to Iran,” announces Reuters; and The National Interest speculates: “The U.S.-Iran Naval War of 2019: What It Could Look Like.”

“The Trump administration continues to double down on a failed policy of confrontation with Iran, rather than diplomacy,” said Pocan. “While it buddies up to dictators around the globe, it threatens peaceful relations in a region that has already seen too much destabilization.”

Pocan has every reason to be concerned. The experienced counselors who initially advised an ill-informed and erratic president—former secretary of defense James Mattis and, to a lesser extent, former national-security adviser H.R. McMaster—have resigned. The president is now surrounded by neocon hawks like National Security Adviser John Bolton, political hacks like Secretary of State Mike Pompeo, and military-industrial complex “yes” men like Acting Defense Secretary Patrick Shanahan. This is a circumstance that demands an intervention by the Congress.

Trump, like every member of Congress, has sworn an oath to defend the Constitution of the United States. That oath requires the president and members of the House and Senate to embrace a system of separated powers in which Congress is charged with declaring wars. That system has decayed over the decades since Franklin Roosevelt recognized, even in the perilous period following the December 7, 1941, attack on Pearl Harbor, that he had a duty to obtain the declaration of war that committed the United States to fight World War II.

But it is a system that can and should be renewed. Pocan has been in the forefront of efforts to do so, working with Representative Barbara Lee (D-CA) to end the 2001 Authorization for Use of Military Force, which successive presidents have used as an excuse to avoid seeking congressional approval for military interventions and bombing missions. He has also worked with Representative Ro Khanna (D-CA) to pass a congressional resolution to end US military support for Saudi Arabia’s brutal assault on Yemen.

Now Congress needs to assert its authority with regard to Iran because, as Senator Tom Udall (D-NM) explains, “The ongoing saber-rattling inches us closer and closer to conflict, borrowing from the same playbook that launched us into the failed invasion of Iraq, and endangering our national security, jeopardizing our diplomatic interests and alarming our allies. The consequences of war with Iran would be catastrophic, risking the lives of thousands of Americans while squandering our global reputation, with little chance of improving our long-term security.”

Arguing that “Congress must assert its constitutional authority to halt the march to war,” Udall has introduced the Prevention of Unconstitutional War with Iran Act of 2019, a Senate measure that “restores to Congress the sole power to declare war by prohibiting any funding for an unauthorized attack on Iran, thereby blocking the president from provoking an unnecessary military conflict in the Middle East.” It’s a bipartisan proposal, co-sponsored by Republican Senator Rand Paul of Kentucky, as well as Democratic presidential contender Bernie Sanders. A parallel measure in the House has been sponsored by Representative Anna Eshoo (D-CA).

Pocan says Congress cannot be “a bystander” when it comes to checking and balancing the imperial impulses of presidents. That’s always true. But in this moment of saber-rattling by Donald Trump and John Bolton, however, that argument becomes far more necessary—and far more urgent.