She actually said it, out loud.

Hillary Clinton has grasped what has long been the prickliest nettle in US diplomacy and directly linked Saudi Arabia to the funding of terrorism.

Only a few weeks ago, the topic appeared taboo.

"I'm not commenting," was Clinton's full stop to questions about whether to declassify official investigations into the Saudi role in the 9/11 attacks.

And when Malcolm Turnbull put the question to Barack Obama last year, asking "aren't the Saudis your friends?", a wry Obama smiled.

"It's complicated," the President was reported to have said.

But after the Orlando massacre at a gay nightclub, the worst mass shooting in modern US history, the Saudi role in promulgating Islamist hate around the world is suddenly on the table.

It's not that we didn't know. The WikiLeaks disclosures showed right back in Clinton's days as secretary of state that she was secretly savage about Saudi reluctance to stem the flow of private cash to extremist groups.

But saying so publicly will be cheered by many people who long wondered why the US has stayed so cosy with the oil kingdom, especially given that 15 of the 19 hijackers on September 11, 2001, were Saudi citizens.

Osama bin Laden was also the scion of a wealthy Saudi family and the nexus with US foreign policy has served as a power socket for conspiracy theories for years.

But as if to prove the ties are still "complicated", Clinton couldn't quite bring herself to single out Saudi Arabia.

"It is long past time for the Saudis, Qataris and Kuwaitis and others to stop their citizens from funding extremist organisations," she declared in the aftermath of the Orlando attack.

"And they should stop supporting radical schools and mosques around the world that have set too many young people on a path towards extremism."

It may turn out Clinton's remarks are premature - at least as far as what motivated Orlando gunman Omar Mateen, whether he was indeed an Islamist radical or just wanted to associate himself with a cause.

Still, for Clinton to even link Saudi Arabia to extremism at all marks what has become a revolutionary realignment in US diplomacy in the Middle East.

For Obama to have questioned the Saudi funding of fundamentalist Wahhabi religious schools in far-off countries such as Indonesia is one thing, given he is near the end of his presidency.

Coming from Clinton, potentially about to begin hers, the criticism will sting.

Saudi Arabia is already upset about Obama's nuclear bargain with Iran, and deliberately timed the execution of a prominent Shiite cleric for January, just as the deal came into force.

This despite the US turning an official blind eye to the Saudi crackdown at home and in neighbouring Bahrain during the Arab Spring.

A number of US conservatives have also questioned the tilt in the Obama years away from Saudi Arabia - although notably not Donald Trump, who has been willing with his criticism of the oil sheikhs.

With the US no longer as dependent on Saudi oil for its energy needs, and the malignant role of Saudi money in extremism now open slather, expect the pressure on one of the world's most repressive regimes to grow.