U.S. Sens. Angus King and Susan Collins of Maine are known for their thoughtfulness and deep background on foreign policy issues. But last week they were faced with a stark choice between enabling a brutal regional client and respecting basic human rights. They came down on opposite sides.

On June 13, the Senate voted on Joint Resolution 42, which would have blocked sales of smart bombs to Saudi Arabia unless it demonstrated it was protecting civilians and allowing free movement of humanitarian aid during its military campaign in Yemen against the Houthi rebels who control most of the country. Saudi Arabia also would have to show it is combating al-Qaida and Islamic State militants.

The bipartisan resolution emerged from concerns that the Saudi air force is dropping American-made bombs on schools, hospitals, markets, ports and bridges, and inciting a massive famine by blockading food shipments to Yemeni ports held by the Houthi. Furthermore, al-Qaida may be benefiting significantly from the Saudi military operation against their common enemy, the Shiite Houthi rebels. The terrorists may be receiving American arms from and even fighting side by side with the Saudi-led coalition.

Forty-seven senators voted to block these sales, including most Democrats, a small group of anti-war Republicans led by Rand Paul, and independent King. But 53 senators voted against, allowing the arms sales to go forward. Among them was Collins.

A year ago King voted against a similar resolution to block arms sales to the Saudis. But the awful human toll of the Yemen war seems to have changed his mind, with 7 million people on the edge of starvation and a child dying every 10 minutes from preventable disease.

At a foreign policy lecture he gave at Colby College in April, I asked his position on arming the Saudis. He said gravely, “I think it’s a mistake … we need to really have deep thought before we get further engaged, and I think we should have a review of our current policy. Because we can’t be complicit. We can’t avoid our responsibility by saying that we don’t know where that jet fuel went.” (King is referring to the U.S. Air Force’s aerial refueling of Saudi jets.)

King is well aware that Saudi Arabia is a key ally to the United States, whose confidence in our alliance was shaken after President Barack Obama signed the Iran nuclear deal in 2015. But he does not believe that we should reassure them of our support at the price of starving to death Yemeni children. And he doesn’t want their war to distract us from confronting terrorism in the region. “We may not be sympathetic to the Houthis or Iran, but nobody likes ISIS,” he told CNN in 2015.

This suggests that he believes the warning of his Senate colleague Chris Murphy, who co-sponsored the resolution to block the arms sales: “If you are interested in radicalizing the Yemeni population against the United States and pushing them into al-Qaida’s arms, then continue to sell weapons to Saudi Arabia.”

But Collins was swayed by neither blood-curdling reports of Saudi war crimes nor the concerns that we are strengthening the hand of our terrorist enemies in the Arabian Peninsula. Given her strong stances on combating terrorism, what could have motivated her vote?

The answer is Iran.

Collins belongs to a dominant foreign policy bloc in the Senate that thinks any action is justified if it helps us “contain Iranian mischief.” In opposing the nuclear deal in 2015, she described how Tehran sows chaos in the Middle East: “Whether it is Hezbollah in Lebanon, the Shiite militias in Iraq, or the Houthis in Yemen, Iran’s proxies are terrorizing innocent civilians, forcing families to flee their homes, and causing death and destruction.”

The senator is right that the Houthis have victimized civilians by shelling residential neighborhoods, kidnapping and executing critics, and obstructing movement of aid. But why is she so indifferent to the massive suffering caused by our Saudi allies, who have done the most to push Yemen into a humanitarian catastrophe? Is her outrage over human rights violations reserved for instances when it intersects with America’s cold-blooded regional interests?

Collins’ blinkered view of the conflict is best summed up by her colleague U.S. Sen. John McCain. When asked last week whether he had human rights concerns about Saudi conduct in Yemen, McCain said, “I’m very worried about Iranian conduct in Yemen.” When asked again, McCain responded, “I’ve answered all your questions.”

During the debate over Resolution 42, leading Republicans stated that selling the Saudis smart bombs would make their attacks more accurate, thus lowering civilian casualties. They should have listened to their colleague Rand Paul, who said of such deadly airstrikes: “This was no mistake, there was no error. This was them pointedly dropping the bombs on civilians.” Just days after the vote the Saudi air force proved him right by killing 25 civilians in a crowded market in the rebel-held city of Saada while they were buying food to break the Ramadan fast.

Furthermore, characterization of the Houthis as simple proxies for Iran is misguided. Tehran has sent small arms and possibly military advisers to the Houthis, and supports them rhetorically. But this assistance is a tiny fraction of their support for Shiite militias in Lebanon, Iraq and Syria, and it is much less important than the fact that much of the Yemeni army crossed over to the Houthi side. Washington and Riyadh are confronting Iran most forcefully in the one place it is engaged the least — perhaps because they know the risk of inciting an actual war is limited. But millions of Yemeni civilians are paying the price for this symbolic posturing.

King and the 46 other senators who voted for Resolution 42 demonstrated that awareness of the Yemen war’s terrible human toll is growing in our capital. But Collins helped create a slim majority that is willfully denying crimes against humanity. Soon a parallel resolution will go before the U.S. House of Representatives for a vote. U.S. Rep. Chellie Pingree has come out strongly against supporting the Saudi military campaign. Will U.S Rep. Bruce Poliquin repeat Collins’ error, which is so costly to the people of Yemen?

Brian Milakovsky is from Somerville, and he works at a humanitarian organization in eastern Ukraine. He blogs at http://yemenmaine.blogspot.com/ and on Facebook at Maine for Yemen.