The U.S. Senate voted 63 to 37 on Wednesday to clear the way for a debate and final vote on a resolution to end American military support for the Saudi-led war in Yemen. It’s the first time that an anti-war resolution has advanced in Congress since Saudi Arabia and its allies intervened in Yemen’s civil war in early 2015.

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The vote, with an unexpectedly wide margin in a Senate typically gridlocked along partisan lines, underscores growing anger over American involvement in a war that is currently the world’s worst humanitarian crisis. But the vote, in which 14 Republicans joined all 49 Senate Democrats, was also a rebuke to President Donald Trump for doubling down on his support for Saudi Arabia’s Crown Prince Mohammed bin Salman, after Saudi agents murdered the dissident journalist Jamal Khashoggi inside the kingdom’s consulate in Istanbul.

Despite the initial Senate vote, the resolution may not ultimately be approved in its current form. Senators could demand amendments or change their minds before a final vote, and Trump has threatened a veto. Saudi Arabia and its allies are also poised to lobby behind the scenes to curtail the measure. And even if the United States ultimately withdraws its support, the Saudi coalition could continue the war for some time. But the vote was a setback for both Trump and Saudi leaders, who are trying to contain the fallout from Khashoggi’s murder.

The Trump administration made a last-ditch effort on Wednesday to derail the vote, by sending Secretary of State Mike Pompeo and Defense Secretary Jim Mattis to give all senators a classified briefing on the Yemen war and Khashoggi’s murder. That move backfired because the White House blocked CIA Director Gina Haspel from testifying at the briefing, as many senators had wanted.

The CIA has reportedly concluded with “high confidence,” after reviewing intelligence intercepts and other evidence, that Prince Mohammed ordered Khashoggi’s killing, despite the Saudi government’s denials of the heir apparent’s involvement. Haspel has listened to audio recordings provided by the Turkish government of Khashoggi’s killing, and senators wanted to question her on the CIA’s assessment of the prince’s culpability. Trump has rejected the CIA’s assessment, and stood by his Saudi ally. In an extraordinary statement on Nov. 20, Trump wrote, “It could very well be that the Crown Prince had knowledge of this tragic event – maybe he did and maybe he didn’t!”

Congress members from both parties are furious at Trump’s unwavering defense of Riyadh, and especially the brash and ruthless 33-year-old prince, a major architect of the Yemen war against Houthi rebels. That anger is finally translating into action to limit U.S. involvement in the Yemen conflict and to potentially restrict American arms sales to Riyadh, which has become the largest buyer of U.S. weapons. (Between 2013 and 2017, Saudi Arabia accounted for 18 percent of all U.S. arms sales.)

One of Trump’s most prominent Republican supporters, Senator Lindsey Graham of South Carolina, even threatened to block the administration’s judicial nominees and legislative agenda until Haspel was allowed to brief the Senate. Graham also warned that if the briefing reinforces the notion that the crown prince was behind Khashoggi’s murder, “there will be no more business as usual with Saudi Arabia.”

In March, Graham and other senators defeated a similar resolution to limit U.S. involvement in the Yemen war, which had won only 44 votes in support. The change in attitude for Graham and other senators who normally support Trump shows that Congress now has an opening to force the administration’s hand on the Yemen war. On Nov. 10, the administration announced it was ending one of the most critical elements of U.S. military assistance: the refueling of Saudi warplanes in Yemen. But that wasn’t enough to appease members of Congress – or to stop the conflict.

The Senate measure, which could be debated as early as next week, invokes the 1973 War Powers Act, arguing that Congress never authorized American military assistance for the Saudi coalition. During the debate, the resolution could be amended and could lose support from some who voted to advance it past the first procedural hurdle. Even if the measure is ultimately approved by the Senate, the House of Representatives would also need to pass a similar bill. In addition, Trump has threatened to veto any legislation that constrains his administration’s ability to support the Saudi coalition.

The war’s full impact has been partly obscured because the United Nations stopped counting civilian deaths in August 2016, when the toll reached 10,000. Many news reports still rely on that outdated figure, even though the actual death toll is far higher. An independent estimate by the Armed Conflict Location & Event Data Project, concluded that more than 57,000 people have died since January 2016.

That estimate also does not the capture the full scope of the human suffering in Yemen. On Nov. 20, the aid agency Save the Children released an analysis estimating that 85,000 children have likely died of hunger since Saudi Arabia and its allies began their bombing campaign in March 2015. “For every child killed by bombs and bullets, dozens are starving to death and it’s entirely preventable,” the group’s country director, Tamer Kirolos, said in the report. “Children who die in this way suffer immensely as their vital organ functions slow down and eventually stop.”

Khashoggi’s murder crystallized U.S. public anger toward Saudi actions – and the slow-bubbling anxiety in Congress over incidents like the Saudi coalition’s bombing of a school bus in the northern town of Dahyan. That attack in August killed 54 people, 44 of them children, and wounded dozens, according to Yemeni health officials. As the scope of the humanitarian crisis in Yemen becomes clearer, Congress has finally decided to act, even if some of its members are more driven by a desire to punish Saudi leaders for the brutal killing of a journalist.