In his speech to the United Nations General Assembly this week, President Donald Trump signaled to Saudi Arabia that he would avoid criticizing its destabilizing actions in the Middle East. Instead, he blamed only Iran, the kingdom’s regional rival, for funding “havoc and slaughter.” Trump praised Saudi Arabia and the United Arab Emirates (UAE) for pledging billions in aid and “pursuing multiple avenues to ending Yemen’s horrible, horrific civil war.” He failed to mention that Yemen’s current conflict escalated dramatically in early 2015, when Saudi Arabia led a coalition of Arab countries to intervene in the war.

That war has long since devolved into a humanitarian catastrophe. The United Nations stopped counting its civilian death toll two years ago, when it hit 10,000. An independent estimate by the Armed Conflict Location & Event Data Project, which tracks conflicts worldwide, found that nearly 50,000 people, including combatants, died between January 2016 and July 2018. The war has also left more than 22 million people—75 percent of the population of Yemen, already one of the poorest countries in the world—in need of humanitarian aid.

As public anger over America’s role in the Saudi-led war against the Houthi rebels in Yemen has grown, Congress has slowly tried to exert pressure on America’s longtime allies to reduce civilian casualties. Last month, a bipartisan group of lawmakers included a provision in the defense spending bill requiring the Trump administration to certify that Saudi Arabia and the UAE are taking “demonstrable actions” to avoid harming civilians and making a “good faith” effort to reach a political settlement to end the war. Congress required the administration to make this certification a prerequisite for the Pentagon to continue providing military assistance to the coalition. This assistance, much of which began under the Obama administration, includes the mid-air refueling of Saudi and Emirati jets, intelligence assistance, and billions of dollars-worth of missiles, bombs, and spare parts for the Saudi air force.

On September 12, Secretary of State Mike Pompeo assured Congress that the coalition was trying to minimize civilian casualties and enable deliveries of humanitarian aid to Yemen. Yet his claim contradicted virtually every other independent assessment of the war, including a recent report by a group of United Nations experts and several Human Rights Watch investigations that alleged the coalition had committed war crimes. Meanwhile, in a memo Pompeo sent to Congress, he noted another reason for continued U.S. support for the coalition: containing Iran and its influence on the Houthis.

Like the Saudis and Emiratis, the Trump administration sees in the Houthis the same sort of threat as other Iranian-backed groups like Hezbollah, which has sent thousands of fighters to help Bashar al-Assad’s regime in Syria. In late August, the U.S. Mission to the United Nations tweeted a photo that had circulated in the Arab press of a meeting in Beirut between Hezbollah leader Hassan Nasrallah and Houthi officials. U.S. officials claimed it showed “the nature of the regional terrorist threat,” and added: “Iranian proxies in Lebanon & Yemen pose major dangers to peace & stability in the entire Middle East.” But beyond recent missile attacks on Saudi Arabia—in retaliation for Saudi airstrikes—the Houthis have displayed little regional ambition. Ironically, as the war drags on, the Houthis will grow more dependent on support from Iran and its allies.

By accepting the coalition’s cosmetic attempts to minimize civilian casualties, the Trump administration is signaling to Saudi and Emirati leaders its apparent belief that a clear military victory in Yemen remains possible. And as long as the coalition believes it can crush the Houthis, there’s little incentive for it to negotiate. Trump, then, has bought into Saudi Arabia’s zero-sum calculation: that a military win in Yemen for the kingdom and its allies would be a defeat for Iran, while a negotiated settlement with the Houthis would be a victory for Tehran. Blinded by its obsession with Iran, the Trump administration is perpetuating an unwinnable war and undermining the likelihood of a political settlement.

This current phase of the conflict in Yemen began in September 2014, when the Houthis, a group of Shia rebels allied with Yemen’s ousted dictator Ali Abdullah Saleh, forced most of President Abdu Rabbu Mansour Hadi’s government to flee to Saudi Arabia, and threatened to take over much of the country. In 2015, the Saudi-led coalition went to war in Yemen to restore Hadi to power and roll back the Houthis. Since then, despite thousands of airstrikes and an air and naval blockade at a cost of some $5 to $6 billion a month for Riyadh, the Saudi-led alliance failed to dislodge the Houthis from the capital, Sanaa.

While the Saudis are quick to blame Iran for the war, several researchers, including Thomas Juneau, a professor at the University of Ottawa and a former analyst at Canada’s Department of National Defense, have shown that the Houthis did not receive significant support from Tehran before the Saudi intervention in 2015. Iran has stepped up military assistance to the Houthis since the war, and Hezbollah has begun sending military advisers to train the Yemeni rebels. But the costs of this assistance fall far short of those incurred by Saudi Arabia and its allies. For Iran, the Yemen conflict is a low-cost way to bleed its regional rival.

The Saudis and Emiratis have largely ignored international criticism of civilian deaths and appeals for a political settlement—and the Trump administration’s latest signal of support shows that strategy is working. Investigations by the UN and other bodies have found both the Houthis and the Saudi-led coalition responsible for potential war crimes. But airstrikes by the Saudis and their allies “have caused most of the documented civilian casualties,” the UN concluded in a report last month. On August 9, the Saudi coalition bombed a school bus in the northern town of Dahyan, killing 54 people, 44 of them children, and wounding dozens, according to Yemeni health officials.

For weeks, the coalition defended the airstrike, but on September 1—with the deadline looming for the Trump administration to certify Saudi and UAE efforts to reduce civilian casualties—the coalition admitted that the bombing was a mistake and it would “hold those who committed mistakes” accountable. U.S. officials seized on that statement as evidence that the Saudi coalition is willing to change its behavior. But for three and a half years now, there has been “little evidence of any attempt by parties to the conflict to minimize civilian casualties,” said Kamel Jendoubi, chair of the UN investigation team that documented war crimes.

The Trump administration has shown little interest in using arms deals as leverage for a political settlement, or to force the Saudis to take concerns about civilian deaths more seriously. In March 2017, Trump reversed a decision by the Obama administration to suspend the sale of over $500 million in laser-guided bombs and other munitions to the Saudi military. As more members of Congress expressed criticism of Saudi actions in Yemen, the Senate narrowly approved that sale. After the Houthis fired ballistic missiles at several Saudi cities in late 2017, the Trump administration again escalated U.S. involvement in the war. The New York Times broke the news that the Pentagon had secretly dispatched U.S. special forces to the Saudi-Yemen border, to help the Saudi military locate and destroy Houthi missile sites. Frustrated by the deepening U.S. role, two dozen members of the House introduced a resolution this week invoking the 1973 War Powers Act, arguing that Congress never authorized American support for the Saudi coalition and instructing Trump to withdraw U.S. forces.

Saudi and Emirati leaders want a clear-cut victory in their regional rivalry with Iran, and they have been emboldened by the Trump administration’s unconditional support to stall negotiations. A recent UN effort to hold peace talks between the Houthis, Hadi’s government, and the Saudi-led coalition collapsed in early September, after the Houthi delegation did not show up in Geneva. Houthi leaders said the Saudis, who control Yemen’s airspace, would not guarantee their safe travel. Days later, Yemeni forces loyal to the Saudi-UAE alliance launched a new offensive aimed at forcing the Houthis out of Hodeidah port, which is the major conduit for humanitarian aid in Yemen. UN officials warn that a prolonged battle for the port and its surroundings could lead to the death of 250,000 people, mainly from mass starvation.

After the Trump administration’s endorsement this month, the Saudi-UAE alliance has even less incentive to prevent civilian casualties and new humanitarian disasters. Saudi Arabia and its allies are more likely to accept a peace process if it is clear that the United States won’t support an open-ended war in Yemen and won’t provide the military assistance required to keep the war apparatus going. But Trump has shown little sign of pressuring his Saudi and Emirati allies, least of all over Yemen. The only realistic check left is in Congress, where more voices are asking why the world’s most powerful country is helping to perpetuate the world’s worst humanitarian crisis.