Earlier this month, 40 Yemeni schoolchildren and 11 adults were killed by a bomb—one that has a legible genealogy. As CNN reported, it was a 500-pound laser-guided MK 82 bomb. And while Saudi Arabia was responsible for dropping it on a school bus, the United States was responsible for providing it: Lockheed Martin built the MK 82, which the U.S. sold to Saudi Arabia as part of an arms deal. America began assisting Saudi Arabia’s campaign in Yemen in 2015, a policy approved by President Barack Obama, and there have been several mass atrocities since then. CNN said the bomb used on August 9 was “very similar” to one dropped on a funeral in October 2016, killing 155 people. (According to Human Rights Watch, pieces of a U.S.-made bomb were found at the site.) In March 2016, a Saudi attack on a Yemeni market killed 97 people. That bomb came from the U.S., too.

Saudi Arabia’s rationale for intervention is straightforward: The Sunni royal family backs the Yemeni government against the Shiite Houthi rebels, who allegedly are backed by Iran. The rationale holding a supportive coalition of Western nations together isn’t quite so clear. Nevertheless, both major political parties in America maintain an overall commitment to the policy, though their justifications for doing so differ. “The only reason that I can guess why the United States continues to arm, train, and provide essential logistical support for the air campaign in Yemen, is that this support has occurred during both Democratic and Republican administrations,” Micah Zenko recently wrote for Foreign Policy. “As we learned in Vietnam previously and Afghanistan every day, where poor strategic decisions are made and sustained by administrations of both major political parties, there is no political advantage for the party out of power to critique current policy.”

According to Zenko, based on off-the-record comments to him, Trump officials justified the policy as a means to check Iranian might. In likewise off-the-record remarks during the Obama administration, officials had cited a need to shore up international support for the Iran deal. If Zenko’s characterization is accurate, the latter excuse helps explain the politically difficult position Democrats are in today. Whatever Obama’s reasons, his failure to end America’s multi-pronged forever war led to this point—to “a litany of war crimes,” as Zenko put it. Trump took the broad strokes of Obama’s foreign policy—the Saudi military alliance in the Middle East, the continued presence of thousands of troops in Afghanistan, drone strikes in Iraq, Syria, and elsewhere—and expanded them, further committing the U.S. to a policy that shows few signs of success. And he’s done so without consistent opposition from Democrats.

The Democratic Party has never been an anti-war party, and it seems unlikely to unite today around an alternative to interventionism. Ending assistance to Saudi Arabia’s campaign in Yemen would be an implicit rejection of part of Obama’s legacy, and it could demand a substantive reordering of the party’s foreign policy priorities. There’s no way to to pull out of the coalition without jeopardizing American relations with Saudi Arabia, and despite plenty of evidence that Saudi Arabia isn’t a reliable ally, the prospect of a fractious relationship with the wealthy petrostate might be enough to dissuade Democrats from changing course. Perhaps that’s why ten Senate Democrats blocked a bipartisan resolution, introduced in March by senators Bernie Sanders, Chris Murphy, and Mike Lee, to pull the U.S. out of the Saudi-led coalition.

Not that Democrats are united in a commitment to Saudi Arabia. In fact, some 2020 frontrunners are taking steps to establish themselves as critics of America’s role in the coalition. The Intercept reported last week that Senator Elizabeth Warren has demanded clarification from General Joseph Votel of U.S. Central Command about his congressional testimony in March, when he told Warren that the U.S. did not track the actions of Saudi planes after the U.S. refuels them and that he did not know if Saudi forces used American-made munitions. (Further reporting by The Intercept undermined both of Votel’s claims.) Warren and Senator Kamala Harris supported the Sanders/Murphy/Lee resolution. There are signs, too, that the two senators are at least skeptical not just of American intervention in Yemen, but of the U.S. government’s military spending; all three, plus Sanders, joined seven other senators to vote against the most recent National Defense Authorization Act.

But if the Democratic Party internalizes the lessons of Yemen, it will have to do more than end munitions sales to Saudi Arabia. It will have to rethink its entire foreign policy. The war crimes in Yemen are just recent entries in an older series of interventionist failures, and previous Democratic presidents bear responsibility for the consequences. Rather than pull troops out of the war in Afghanistan, Obama kept them locked in a protracted conflict that turned 17 this year. Children born after the September 11 attacks will soon be old enough to fight in a conflict that began before they were born. Iraq, meanwhile, is a state on life support.

“Astonishingly expensive, strategically incoherent, sold by a shifting slate of senior officers and politicians and editorial-page hawks, the wars have continued in varied forms and under different rationales each and every year since passenger jets struck the World Trade Center in 2001,” C.J. Chivers wrote recently in The New York Times Magazine. “They continue today without an end in sight, reauthorized in Pentagon budgets almost as if distant war is a presumed government action.” Trump could well make the situation worse, just as he’s done in Yemen: NBC News reported on Friday that Trump has shown “renewed interest in a proposal by Blackwater founder Erik Prince to privatize the war” in Afghanistan, though the White House denied this in comments to the news channel.

Meanwhile, the Trump administration is contemplating future conflicts. In its latest National Defense Strategy, the Defense Department declared that Russia and China are America’s “principal priorities”—despite Trump’s reluctance to criticize the former for its interference in U.S. elections. “Inter-state strategic competition, not terrorism, is now the primary concern in U.S. national security,” the document reads. The forever war may thus expand. If it does, the Democratic Party will be complicit, unless it’s willing to reject not only the foreign policy of its last president, but also its own closely held doctrines.