A game-changing event happened this past Tuesday, and it wasn’t attorney general Jeff Sessions testifying before the Senate Intelligence Committee.

While Sessions was getting grilled, other senators were debating the wisdom of selling a roughly $500 million package of air-to-ground, GPS-guided munitions to the Royal Saudi Air Force—the type of munitions that have laid waste to much of Yemen over the last several years.

The attempt to block the munitions sale—crafted by senators Rand Paul, Chris Murphy, and Al Franken—was defeated by a 53-47 margin. But the fact that a bipartisan group of senators chose to vote in favor of a resolution of disapproval is one of the strongest signals sent from Washington to date that a growing number of lawmakers are concerned about supporting the Saudi-led military campaign in that country.

The civil war in Syria is often documented as one for the bloodiest and nastiest wars that the Middle East has witnessed over the past decade, but Yemen’s conflict is actually worse from a humanitarian standpoint. In addition to the conservative estimate of 8,000 civilians killed and three million displaced from their homes, the combination of poor targeting from the Saudi Air Force and the indiscriminate lobbing of rockets from the Houthis has produced such hardship on the country’s civilians that one wonders why more haven’t chose to take refuge somewhere else.

Before the civil war, Yemen was had the ignobility of being the Middle East’s poorest nation. Over 68% of Yemen’s entire population requires some form of humanitarian assistance from the international community and 17 million are considered to be food insecure by the World Food Program considers to be food insecure—3.3 million of whom are either children or pregnant women. In the over two years since the civil war erupted into a proxy conflict pitting a Saudi-led Arab coalition against a Houthi movement that is at times supported by Iran, Yemen has effectively ceased to exist as a nation-state.

No one put it better than Stephen O’Brien, the UN undersecretary general of humanitarian affairs, when he briefed the UN Security Council last month on the dire humanitarian situation. “The people of Yemen are being subjected to deprivation, disease and death as the world watches,” O’Brien said. “That is not an unforeseen or coincidental result of forces beyond our control. It is a direct consequence of actions of the parties and supporters of the conflict. It is also sadly a result of inaction, due to inability or indifference, by the international community.”

Indeed, the parties to the conflict have been—and remain—oblivious to the civilian suffering that has been occurring. Based on the statistics, it’s not all unreasonable assumption that many of the men in the air searching for enemy targets or prowling around on the ground with guns slung over their shoulders don’t care if civilians are killed in the crossfire, particularly if a military objective is achieved.

The Houthis, a group that swept into the Yemeni capital in September 2014 with the crucial assistance of former Yemeni leader Ali Abdullah Saleh’s loyalists, have employed tactics that would sound eerily similar to Bashar al-Assad’s butchery in Syria. UN relief convoys are routinely stopped at Houthi checkpoints and turned away, not because the security environment is too volatile for the aid workers distributing the assistance, but rather because Houthi fighters hope to put as much pressure on besieged pro-government units as possible. Houthi rockets and ballistic missiles launched across the border into Saudi Arabia have killed dozens of Saudi civilians, a development that has prompted even harsher retaliatory measures from the Saudis.

And yet as barbaric as the Houthis have been, the actions of the Saudi air force have been even more detrimental to Yemen’s civilian population. Multiple reports from the UN Security Council’s own Panel of Experts, from the UN High Commissioner for Human Rights, and from various human rights organizations have documented in extensive detail the destruction left in the wake of Saudi Arabia’s bombing missions. The same civilian structures that are supposed to be off-limits during combat operations have been struck repeatedly since Riyadh commenced major air operations in March 2015. While it’s incredibly difficult to quantify the toll in an ongoing war, the Yemen Data Project —a group composed of scholars and human rights activists—has found that of the 8,600 air attacks that the Saudi coalition conducted from March 2015 to August 2016, 3,158 struck non-military targets. In other words, over 36% of the coalition’s airstrikes have hit structures like schools, hospitals, medical clinics, refugee camps, markets, and mosques that are outside the confines of what is a military target under the Geneva Conventions.

None of this even begins to account for the naval and air embargo that the Saudi coalition has enforced in Yemen, which has slowed the shipment of humanitarian aid, food, water, medical equipment, and fuel to a trickle. An embargo would put any nation under severe strain, but the policy is particularly dangerous policy in Yemen, a country that depends on its sea and airports to import 80-90% of its food supplies.

Where does the US fit into all of this? It’s simple: they have been by far the largest supplier of weapons and bombs to the Saudis since the conflict began. Washington may not be a direct participant in the war in the traditional sense of the word—there are no conventional soldiers clearing Houthi combatants in Yemen’s major cities—but that doesn’t mean that the US is an inactive bystander either. It would be logistically difficult for Riyadh and its allies in the Gulf to sustain their combat operations without the smart bombs, fighter and bomber aircraft, and mid-air refueling capability that President Barack Obama and now President Donald Trump have offered.

A war that has no military solution is in all practicality being kept afloat by US-supplied munitions, dropped from US-manufactured planes, fueled by US tanker aircraft. Lawmakers who have frequently spoken out in opposition against US involvement—senators Paul and Murphy in particular—are understandably confused as to what national security interests Washington is protecting by picking sides in a Middle Eastern proxy war. Apart from the usual platitudes about supporting and assisting an ally in the region, the administration has yet to provide any good answers.

Nine months ago, Rand Paul and Chris Murphy forced their fellow senators to come to the floor and debate whether selling M1A1/A2 Abrams tanks to the Saudi military would serve the US national security interests in the Persian Gulf. Their resolution of disapproval was killed in a 71-27 vote, a margin that Riyadh could look upon as a comfortable victory. This week’s disapproval motion, however, should make the Saudis nervous; proponents of stopping the sale of bombs to the Saudi air force and holding the Saudi leadership accountable for its conduct picked up notable support from senior lawmakers who in the past endorsed the Saudi position.

Senators Chuck Schumer, Ben Cardin, Chris Coons, Angus King, and Jack Reed, senators who voted to affirm Saudi weapons requests during a similar vote last September, switched their positions. In a town that normally provides Saudi Arabia with whatever weapons system it wants with very little pushback (minus a few exceptions, like the F-35 fighter), the shift is a public demonstration of just now increasingly agitated Republicans and Democrats alike are about the humanitarian consequences of the war in Yemen and how the Saudis and their partners are managing their campaign.

President Donald Trump, who seems to be especially eager to cement a positive relationship with the Saudi Royal Family, reportedly lobbied on behalf of the $500 million defense package. Legislatively, he proved to be victorious—a small notch on his belt at a time when his legislative priorities have been bottled up on Capitol Hill. Trump, however, shouldn’t take solace in the fact that the bombs are now in their crates, ready to be shipped across the Atlantic Ocean. Nearly the entire Senate Democratic caucus and at least four members of the Senate Republican majority are no longer willing to ignore the incontrovertible evidence that it out there: the Saudi air force has been in the most generous assessment clumsy and incompetent throughout the operation; the war in Yemen is enveloping Yemen in a pot of misery that would make Somalia look like a viable destination; and the conflict won’t get any better as long as the combatants continue to believe that victory can be attained militarily.

How long will it take for president Trump and his national security team to adopt the same view?