How would you explain the long-standing and bizarre alliance between the United States of America and the Kingdom of Saudi Arabia to the proverbial Martian who had landed on Earth for the first time? The close friendship between the secular republic and the Salafist theocracy? The unbreakable bond between the liberal democracy and the absolute monarchy? You would probably have to begin by going back to February 1945. That’s when Franklin D Roosevelt met Saudi Arabia’s founding king, Abdulaziz, on-board the USS Quincy in the Suez Canal, to strike a Faustian bargain: Washington would provide the security while Riyadh would provide the oil.

No US president since FDR has deviated even slightly from these terms – not even Barack Obama who, while loathed by the Saudis for his Iran nuclear deal, agreed to sell an unprecedented $115bn worth of weapons to them during his eight years in office. (British governments haven’t been any better: the Saudis have been close allies and major buyers of UK arms since the 1960s and, this summer, Theresa May buried an official report on the foreign funding of extremism which is believed to have highlighted the significant role played by Saudi Arabia.)

See no evil, hear no evil, speak no evil. That’s been the shameless position of Western governments when it comes to the Gulf kingdom. Successive US administrations, Democrat and Republican, have even stayed silent on the supposedly all-important issue of terrorism. Fifteen of the 19 hijackers on 9/11 were Saudi citizens? No problem. “Donors in Saudi Arabia constitute the most significant source of funding to Sunni terrorist groups worldwide,” according to a leaked State Department memo? Don’t worry about it. Islamic State is printing copies of Saudi textbooks to use in their schools? Ssshhhh.

These days, the conventional wisdom is that the Trump administration has revitalised the US-Saudi special relationship. The president – who once suggested the Saudi government was behind 9/11! – made the kingdom the first stop on his inaugural foreign trip in May and then threw his full support behind Crown Prince Muhammad bin Salman’s controversial purge of his royal rivals on 4 November.

Yet the conventional wisdom may be wrong. There are plenty of signs that times are changing. Consider events on Capitol Hill. In September 2016, a bipartisan bill in the Senate to stop the sale of more than $1bn worth of American-made tanks and other weapons to Saudi Arabia was defeated 71 to 27. Yet, in June this year, a similar bipartisan bill to block the $510m sale of precision-guided munitions to Saudi Arabia was defeated by a much narrower margin: 53 to 47. “Regardless of whether the number is 48 or 51 or 45, this is an important message to the Saudis that we are all watching,” Democratic Senator Chris Murphy, a co-sponsor of the bill, told reporters ahead of the vote. Other senators have gone further. “I consider [Saudi Arabia] to be an undemocratic country that has supported terrorism around the world… they are not an ally of the United States,” Bernie Sanders, a supporter of the Murphy bill and perhaps the single most influential political figure in America right now, told me in a recent interview.

On 13 November, for the first time since the Saudi-led, US-backed bombing campaign in Yemen began in March 2015, the House of Representatives voted 366 to 30 in favour of a controversial resolution. It noted how “Congress has not enacted specific legislation authorising the use of military force against parties participating in the Yemeni civil war” and denounced the “deliberate targeting” of civilians. The (non-binding) resolution also pointed out that the US has “provided midair refuelling services to Saudi-led Arab Coalition warplanes” and that “at least 10,000 Yemeni civilians have been killed in this conflict since 2015”.

Co-sponsor Congressman Ro Khanna, a Democrat from California, tells me he is outraged by the Saudi-induced “humanitarian catastrophe” in Yemen. “Why in the world is the United States aiding the bombing of a civilian population which is leading to outbreaks of cholera and famine?”

Khanna does not advocate any sort of confrontation with Riyadh but thinks the US “certainly should not be doing their bidding”. Such increased hostility from legislators, combined with the growing number of anti-Saudi op-eds in the American press, is perhaps part of the reason why Riyadh, as reported by the Financial Times, plans to set up new public relations “hubs” to “improve international perception of the kingdom”. It may also help explain the rather cynical timing of the Saudi king’s recent decision to lift the ban on women drivers.

But can a PR offensive save the House of Saud, which has beheaded far more people than Islamic State? How long are US politicians and pundits expected to turn a blind eye to Saudi support – both ideological and financial – for some of the worst “jihadist” groups? “How can you be allied with a regime that is exporting terrorism?” asks Khanna. The Saudi vision of Islam, he adds, “is against pluralistic, liberal, open values”.

Khanna is well aware of the influence of the Saudi lobby, which he acknowledges has “built relationships” with power players across Washington DC and helped cement the seven-decade alliance between the two countries. Nevertheless, he has a clear message for Riyadh. “There is a growing sentiment on the right and left that we should hold Saudi Arabia more accountable,” Khanna says, referring to his colleagues on Capitol Hill. “We’re not going to give up.” The Saudis can’t say they weren’t warned.