Donald Trump was expected to refuse to recertify the Iran nuclear deal. He did that on Friday.

But the president did much more than signal his personal disapproval of Tehran’s compliance with an agreement that the Obama administration and international allies reached in 2015 to avert the development of nuclear weapons by the Iranians. In a bombastic address, Trump pointed toward a dramatic ramping up of hostility toward a country that international observers and even his own aides indicate has been in compliance with the nuclear deal.

The president’s pronouncements on Friday were not merely at odds with the facts regarding the agreement. They steered the United States away from diplomacy and toward a more charged—and potentially far more dangerous—relationship with Iran. They also distanced the United States from its allies. As former vice president Joe Biden explained on Friday, “Unilaterally putting the Iran deal at risk does not isolate Iran. It isolates us.”

Trump did not seem to recognize that prospect, let alone to understand the consequences of a go-it-alone strategy that will make the United States an international outlier.

In his televised speech to the nation Friday, the president said he wanted Congress to set new benchmarks that Iran would be required to meet in order to avoid nuclear-related sanctions. He bluntly declared that the deal “will be terminated” if no plan is reached to radically alter the agreement.

The president’s over-heated language was decried by serious observers of the deal and of US relations with Iran. “Make no mistake: With his announcement today, President Trump is putting America at risk,” announced Senator Jeff Merkley (D-OR), who explained that:

Most immediately, this reckless decision could give Iran a path to back out of the nuclear deal and resume its race to a nuclear bomb. A nuclear-armed Iran could become the single greatest national security threat we face and would be an immediate existential threat to Israel. At a time when our own intelligence agencies and every international monitor says that Iran is in compliance with the strict limits and monitoring of the JCPOA (Joint Comprehensive Plan of Action), blowing up this agreement is the definition of a self-inflicted wound.

Trump rubbed the wound raw with remarks that pointed toward a significant intensification of US hostility toward Iran. The president accused Tehran of stirring “chaos” in the Middle East and beyond. He labeled the Iranian government as “fanatical regime” and accused it of spreading “death, destruction and chaos around the globe.” Directing the Treasury Department to impose new sanctions on Iran’s Islamic Revolutionary Guard Corps—which the White House identified as a “primary tool and weapon in remaking Iran into a rogue state”—Trump took steps that the administrations of Barack Obama and George W. Bush carefully avoided.

What Trump did Friday was serious, and unsettling. He took steps to alter relationships not just with Iran but with allies of the United States that helped to forge the nuclear agreement.

“The fallout of the U.S. going back on our word will reverberate far beyond just Iran. It will hurt our relationship with our European allies, on whom we rely as critical partners in nearly every aspect of international relations,” said Merkley, who explained that

[At] an absolutely crucial moment, it could torpedo efforts to secure international collaboration to end North Korea’s nuclear program. Why would international partners work with us to impose sanctions on North Korea to bring them to the negotiating table, and why would North Korea come, if they know the United States does not live up to its word?

Congress still has a say with regard to the Iran deal. Indeed, says House Democratic Caucus Vice Chair Linda Sánchez (D-CA), “It is now up to Congress to prevent Donald Trump’s ‘America First’ strategy from turning into ‘America Alone.’”

Congressional Progressive Caucus Co-Chairs Raúl Grijalva (D-AZ) and Mark Pocan (D-WI) promised to organize House opposition to Trump’s position.

“President Trump’s announcement decertifying Iran’s compliance with the JCPOA nuclear agreement—in defiance of eight compliance reports from the International Atomic Energy Agency and the assessment of his own Secretary of Defense—is yet another act of cynicism and deeply reckless political theater,” said the CPC leaders. “Like his recent unilateral decisions to sabotage the Affordable Care Act, the Clean Power Plan, and the U.S. commitment to the Paris Climate Agreement, President Trump once again showcases his willingness to put millions of lives at risk to score cheap political points in undoing the achievements of his predecessor.”

“We must not mince words,” Grijalva and Pocan added:

By rejecting overwhelming evidence of Iranian compliance with the JCPOA, President Trump is putting us on a disastrous path of confrontation and escalation with Iran. Congress needs to reassert its constitutional authorities and serve as a check to a totally erratic and dangerous executive who has already threatened to “totally destroy” another country. We urge our colleagues to vote to reject any re-imposition of sanctions against Iran that result from President Trump’s decision today. The Congressional Progressive Caucus, reflecting the will of tens of millions of Americans who have advocated for peace, diplomacy, and stability, will strongly oppose any legislative or executive effort that seeks to undermine the JCPOA or needlessly ratchets up tensions with Iran, which would also threaten America’s credibility to peacefully resolve tensions with North Korea using diplomacy.

Merkley promised to fight just as hard in the Senate, Merkley saying, “As a member of the Senate Foreign Relations Committee, and as a concerned American, I will do everything I can in partnership with my colleagues to prevent this travesty of a decision from going into effect.”

The congressional critics will have many allies in this vital struggle.

“If the U.S. backs out of the Iran agreement, that would put war with Iran back on the table. At the same time, it would send a terrible signal to North Korea about the U.S.’s ability to stand by its international commitments, which could unravel any hopes of negotiating a similar agreement to scale back North Korea’s nuclear program,” Jon Rainwater, the executive director of the group Peace Action, said Friday. “The ball is now in Congress’ court. Will they listen to the more that 80 nuclear policy experts, key members of Trump’s own administration, and foreign policy leaders from around the world calling on the US to stick with the deal?”

What is certain, said Rainwater, is that the activists who two years ago succeeded in “getting the deal through Congress and preventing a war” must rally once more “to protect that historic achievement.”