President Obama received a rather lukewarm reception from Saudi royals when he landed in Riyadh on Wednesday. Saudi social media commentators noted that he was met with a reception led by the city’s mayor instead of King Salman, who greeted regional leaders with a great deal more gusto right after they landed. Nor did Obama exchange kisses with the Saudi leader, as his predecessor George W. Bush once did.

But the alliance between Saudi Arabia and the United States is not quite what it used to be. Tensions have reached new heights in recent weeks among suggestions that the Kingdom’s money was used to fund the 9/11 hijackers – three-fourths of whom were Saudi nationals. A proposal in Congress that might allow victims of that attack to sue the Kingdom if it’s found to have supported terrorism has further chilled relations. Saudis also feel snubbed by Obama’s suggestion that they could be among the “free-riders” he mentioned in an interview who benefit from the U.S. War on Terror but don’t contribute their fair share to the fight. More open relations with the Kingdom’s sworn enemy Iran haven’t helped either.

Here’s a look at how a once iron-clad alliance is being shaken – and why it’s taken so long to quiver.

How has President Obama’s stance on Saudi Arabia shifted?

In 2002, then State Senator Obama delivered a speech denouncing President George W. Bush’s plans to invade Iraq with the suggestion that he instead focus on the fight against “so-called allies” like Saudi Arabia to insist that they “stop oppressing their own people, and suppressing dissent, and tolerating corruption and inequality.”

Since becoming president, Obama has been forced to defend his support of Saudi Arabia – and his unwillingness to denounce the country’s record on human and women’s rights like he has in other countries. But he’s also called out the Kingdom for not doing enough in the fight against ISIS.

Still, he hasn’t been willing to snub the Kingdom despite his differences with how it conducts itself.

“Aren’t the Saudis your friends?” Malcom Turnbull, the Prime Minister of Australia asked Obama during the Asia-Pacific Economic Cooperation summit in November.

“It’s complicated,” Obama replied with a smile.

Ben Rhodes, a deputy national security adviser, explained some of the complexities in a podcast with former Obama aide David Axelrod:

“For many years, the basic interest at the root of the U.S.-Saudi relationship was that they provided the oil that sustained the global economy and we provided essential security for the Saudi state, and we really didn’t think of any other aspect of it at great length,” he said. “We just kind of thought about security and oil, and we didn’t go that other layer down.”

“A lot of the money — the seed money — for what became al-Qaeda came out of Saudi Arabia,” said Rhodes, who worked on the 9/11 Commission report.

While he wouldn’t say if Saudi officials doled out the cash, he suggested that they might have turned a blind eye to where it ended up: “Certainly there was an insufficient attention to where all this money was going over many years from the government apparatus.”

Have other countries shifted their stance on Saudi Arabia recently?

Yes. The United Kingdom canceled a contract to work on Saudi Prisons in October after a British citizen there was sentenced to be lashed after he was caught with homemade wine. In February, the European Union passed a non-binding measure calling on all member states to cease selling arms to Saudi Arabia due what it described as a “disastrous humanitarian situation.” In March, the Dutch Parliament voted to block arms’ sales to the Kingdom, citing Saudi’s high execution record as well as human rights violations in its airstrikes on neighboring Yemen.

Where does President Obama stand on allowing 9/11 victims and their families’ sue the Saudi government?

He isn’t into it. Obama told CBS News that he would oppose a bipartisan-backed bill that would allow the victims of 9/11 and their families to sue Saudi Arabia if it is found to have been involved in that attack.

“This is not just a bilateral U.S.-Saudi issue,” he said. “This is a matter of how, generally, the United States approaches our interactions with other countries.”

“[I]’s difficult to imagine a scenario in which the president would sign the bill as it’s currently drafted,” White House Press Secretary Josh Earnest told reporters on Monday, reiterating that it wasn’t a U.S.-Saudi issue, but a broader international policy matter. “It could put the United States and our taxpayers and our service members and our diplomats at significant risk if other countries were to adopt a similar law.”

He stressed the importance of “sovereign immunity” for states. That’s an issue that fellow Democrats including Chuck Schumer of New York fundamentally disagree with.

“If Saudi Arabia participated in terrorism, of course they should be able to be sued,” the Senate Democratic Leader said on Monday. “This bill would allow a suit to go forward and victims of terrorism to go to court to determine if the Saudi government participated in terrorist acts. If the Saudis did, they should pay a price.”

Before that can happen, the U.S. will have to establish a clear connection between Saudi officials and the perpetrators of 9/11.

What role did Saudi Arabia play in the 9/11 attacks?

Saudi officials maintain the country didn’t play any role in the attacks.

In 2002, two unidentified Clinton administration said that two Saudi princes paid Osama bin Laden to menace other countries after a 1995 bombing in Riyadh that killed five American military advisers. When asked about those payments, however, a Saudi official responded, “Where’s the evidence? Nobody offers proof. There’s no paper trail.”

The 9/11 Commission also essentially said the country didn’t play a role.

“Saudi Arabia has long been considered the primary source of Al Qaeda funding, but we have found no evidence that the Saudi government as an institution or senior Saudi officials individually funded the organization,” the Commission’s report stated.

The Commission, did not, however, rule out the involvement of Saudi officials and clerics passing the Kingdom’s money off to al-Qaeda without official sanction of the King.

That’s what many believe the now infamous 28 pages from a classified Congressional report will make clear.

On Monday, Obama told CBS News that National Intelligence Director James R. Clapper Jr., will soon complete a review of the report to help decide if could be made public.

What will the economic impact of a fallout with Saudi Arabia be?

Saudi officials have already expressed chagrin at U.S. officials for questioning its merits as an ally – and have even moved to put a monetary sum on their malaise.

Saudi Arabia’s foreign minister warned the Obama administration and members of Congress that they will sell up to $750 billion dollars in American assets if Congress passes the bill that could hold Saudi Arabia accountable for playing a role in the 9/11 attacks.

Economists and analysts have called the warning an “empty threat.”

“It’s proper to note that the figure of $750 billion in U.S. assets may itself be a gross overstatement,” Michael Hiltzik wrote in the L.A. Times’ The Economy Hub blog.

According to Tim Worstall of the Adam Smith Institute in London, the amount is not so huge compared to the overall bond market and would take time to actually sell off, thus softening the blow to the U.S. economy.

“In terms of this being a threat,” he wrote for Forbes, “It just isn’t much of one.”