A bill to block the sale of weapons to Saudi Arabia failed to advance in the Senate on Wednesday as senators voted resoundingly in favor of a $1.15bn arms transfer.

Despite the defeat in the Senate, however, one US senator, Chris Murphy, has pledged to continue his campaign to re-evaluate America’s relationship with the country, a longtime US ally.

“US support for Saudi Arabia’s wars cannot be unconditional, especially when civilians are being killed and terrorist organizations are growing stronger,” Murphy, a Connecticut Democrat, said after the vote. “Congress is watching and we will not sit on the sidelines.”

For the past year, Murphy has continued to call for his colleagues on Capitol Hill to rethink the status quo of American support for the Saudi kingdom. His is a controversial and unpopular position because the country is viewed as a key partner in the Middle East, but it’s one that’s growing in popularity among politicians in Congress and the Senate.

In an interview with the Guardian, Senator Murphy explained that, while he believes the United States’ relationship with Saudi is a vital one, the Gulf state’s activities in Yemen are out of line with US national security interests.

“There has been little to no debate in the US Congress about this country’s participation in civil war in Yemen that’s greatly harming US national security,” he said. “The Saudis are not immune from criticism.”

“My hope is that while so far it doesn’t seem they’ve made any meaningful changes in the way that they conduct their airstrikes, maybe in the wake of this debate, with bipartisan concern shown for the results for aerial targeting, that they’ll change their way.”

Murphy has been willing to question America’s “special relationship” with Saudi Arabia for some time but he laid out his stance most definitively during a speech at the Council on Foreign Relations in January.

In that speech, Murphy said Saudi Arabia’s Wahhabi branch of Islam had an insidious effect in many majority Muslim countries, and it was exported using a “tsunami of money”, which more moderate forms of the religion could not compete with.

“Why has Saudi Arabia been largely immune from direct public criticism from political leaders simply because they are a few degrees separated from the terrorists who are often inspired by the ideology their money helps to spread?” Murphy said at the time. “There’s growing evidence that our support for Saudi-led military campaigns in places like Yemen are prolonging humanitarian misery and aiding extremism.”

Saudi Arabia and a coalition of Arab states began an aerial bombardment of Yemen in March last year to reinstate President Abd-Rabbuh Mansour Hadi, a Saudi ally, after he was pushed out by Houthi rebels. The Saudis consider the Houthis a client of Iran and therefore a threat on their border.

What was intended to be a short-lived campaign, has now entered its 18th month and has spiralled into a humanitarian disaster. Ten thousand civilians have died, food and water shortages have led to more than a million malnourished children, and aid groups’s access to the country has been blocked.

The US has provided military assistance to the Saudi-led coalition in Yemen through intelligence, and help refueling planes while they carry out airstrikes. Barack Obama has also overseen $115bn worth of arms offers to Saudi Arabia during his tenure, more than any other US administration in history.

“There’s an American imprint on every civilian life lost in Yemen,” Murphy told CNN in August. “Because, though the Saudis are actually dropping the bombs from their planes, they couldn’t do it without the United States.”

Beyond the myriad human rights violations in the war in Yemen, Murphy also wants to prevent Saudi Arabia from exporting its fundamentalist view of Islam, Wahhabism, around the world. He said it was creating fertile ground for terrorist groups to recruit impressionable youth.

The Gulf state has also considerably reduced its involvement in the anti-Isis coalition since the war in Yemen started, committing few airstrikes since September 2015, according to IHS Jane. The war in Yemen is creating a vacuum that groups such as al-Qaida and Isis are capitalizing on.

“I don’t think the United States should be in the business of dictating what form of Islam wins out around the world,” Murphy said. “[But] I’d like to see the Saudis be much more careful about this. I’d like to see them be much more careful about the kind of operations that they’re funding abroad.”

Since his speech in January, Murphy and Republican senator Rand Paul have put forward several resolutions aimed at blocking further arms deals with Saudi Arabia as human rights violations persist.

Saudi Arabia’s actions in Yemen have led many western states to reconsider their relationships with the oil-rich state. Countries such as Belgium, the Netherlands and Canada, have all taken some form of action to block weapons transfers. The European parliament passed a non-binding resolution to prevent arms sales, while debate on the topic continues to rage in the UK.

Murphy and Paul’s push in the Senate has also been matched in the House of Representatives. Representative Ted Lieu introduced a bill on Tuesday that matched the senators’ resolution, and has also led a group of vocal opponents of Saudi arms sales in the House.

This is a clear departure from 60 years of a policy geared towards maintaining the special relationship that was strengthened during the cold war due to shared anti-communist goals.

“It shouldn’t be a surprise to anybody that the Saudi embassy is lobbying against my resolution,” Murphy told the Guardian. “It also shouldn’t be a surprise that the Saudis have very deep relationships with a lot of senators and congressmen, they’ve been partners with the United States for a very, very long time.”

The persistent strength of the relationship was evident when Murphy’s bill was blocked by a resounding 71-27 votes.

Senator Lindsey Graham of South Carolina, one of the more hawkish Republicans in Congress, said he was against the measure because “it would be a disaster to sever the relationship with Saudi Arabia”.

Graham, who ran unsuccessfully for the Republican presidential nomination this year, said he was concerned with the humanitarian casualties in Yemen at the hands of the Saudi-led coalition in the region.

“But we have no perfect allies,” he said.

Marco Rubio, the Florida senator and former Republican presidential candidate, said he did not see “a connection between selling tanks and opposing terrorism”.

“Obviously, I have issues with the decisions the Saudi government has made,” said Rubio, who sits on both the Senate intelligence and foreign relations committees.

“But that’s unrelated to selling arms to a nation whose military constantly now appears to be one of the few blocks we have to rein in ambitions in the region.”

Murphy is, however, adamant about the fact that he does not want to end relations with Saudi Arabia.

“I think strong alliance allows for one party to object to the behaviour of the other when it’s not in the party’s mutual national security interests,” he said. “I think our relationship can survive a rethinking of US participation in the civil war.”