Slighted by years of neglect and stunned by the Iraqi military capitulation, Washington has lost faith in the embattled leader

In October 2011, Barack Obama and his national security committee sat down for the most important conference call they had held on Iraq. On the videolink from Baghdad was Nouri al-Maliki, a man whom the US had backed as a second-term leader a year earlier.

Folders and briefing pads were piled in front of the Americans. In Baghdad, Maliki sat with only a translator. He wanted no discussion about an extension of the US presence in Iraq, not even a token contribution for training or mentoring. Maliki's stance was welcomed by many in the room, who viewed Iraq as a politically consuming misadventure.

But they were just as surprised as the hawks at the Iraqi leader's defiance. After eight long years, most of them as partners of sorts, it had come to this; there was no longer anything to negotiate. Maliki's Iraq would go it alone; the US could turn the lights off when it left.

For almost three years since, that seminal meeting has defined the relationship between the Obama White House and Maliki – a rising single-minded strongman and the increasing irrelevance in Iraq of a conquering superpower.

As US eyes turned away from Iraq, Iraqi eyes looked elsewhere for support. Some in Washington began to wonder whether, after almost $1tn (£590bn) and close to 4,500 combat losses, Iraq really wanted a strategic partnership with the US at all. The turmoil surrounding the Arab uprisings put answers to that on hold, for a while at least. It also pushed Maliki towards a deeper relationship with Iran.

With much of the Sunni Arab world in uproar, Maliki wanted the safety in numbers that his Shia neighbours offered. While embracing Iran, Maliki put distance between his government and Iraq's Sunni minority, arresting several tribal leaders, laying siege to a protest camp in Ramadi, and brazenly issuing an arrest warrant for the Sunni former vice-president Tariq al-Hashimi days after US forces left.

He set about co-opting key institutions left behind by the Americans; the Iraqi National Intelligence Service, which was soon stacked with officials from his Dawa party, and Iraq's elite special forces unit, which became his praetorian guard.

Some in Washington started believing that Maliki's moves were consolidating power along nakedly sectarian lines. "It was more out of making sure that power could never be stripped from him," said one senior US diplomat.

Another American official who acted as senior US adviser to the Iraqi government from 2004-11 said: "The only thing that I saw with my eyes that could be construed as sectarian was his appointments, especially in the military." While they were not all sectarian, most were; and the competence of the candidate was not an issue.

Evermore disturbed, Washington protested loudly and made calls for political inclusiveness. But the former occupier no longer had the leverage – or apparently the will – to force Maliki to act.

Today, as the state he tried to build through a ruthless consolidation of power, and a strong dose of paranoia, crumbles around him, critics and foes are circling. First among them is the US. Slighted by three years of neglect and stunned by the three-day capitulation of the Iraqi military, Washington is strongly signalling it has lost faith in Maliki.

The embattled leader has sensed the change in mood and on Wednesday said he would not resign in return for US airstrikes against insurgents.

On Thursday, when asked if Maliki should step aside, Obama said: "It is not our job to choose Iraq's leaders, but I don't think there is any secret that, right now at least, there are deep divisions between Sunni, Shia and Kurdish leaders."

He said the White House had told Maliki that "as long as those deep divisions continue or worsen" the central government would be unable to stem the sectarian crisis engulfing the country.

Obama urged the Iraqis to form a new government, holding out the inducement that it would "make it much easier to partner than it is right now".

The move away from Maliki is precipitous. In testimony to the Senate on Wednesday, the chairman of the Joint Chiefs of Staff, General Martin Dempsey, said repeatedly that the Iraqi government had failed on its commitment to combat sectarianism.

More ominously for a government that urgently seeks US military aid, Dempsey and the defence secretary, Chuck Hagel, told a Senate panel already champing at the bit for the Iraqi prime minister's downfall that military intervention would be futile without concerted action from Maliki to embrace Sunnis.

The reversal is as thorough as it is sudden. Zalmay Khalilzad, the Bush-era US ambassador who assiduously helped install the then-obscure Maliki as leader in 2006, told reporters that Iran could help the US persuade Shia politicians to "make a change" by replacing Maliki. This may yield yet further common ground for the arch foes who, not long ago, fought a vicious proxy war in Iraq, and now seem increasingly drawn together by a common threat.

Iran has yet to declare its hand about who should lead Iraq. However, the Iranian general Qassem Suleimani, long a kingmaker in Baghdad, has an increasingly dim view of Maliki. "He says the man's an idiot," a senior Iraqi politician who met Suleimani last week told the Guardian. "When he was asked about who should lead the country, he didn't say a word."

At the time, Maliki's installation was hailed as "something of a victory for Khalilzad" by Washington Post columnist David Ignatius, who speculated that Maliki's "authentic Iraqi credentials could help pull the country together".

For years that was the prevailing wisdom in Washington, despite mounting evidence that Maliki was a burgeoning authoritarian and Shia supremacist. The Bush administration, yoked to him for the 2007 troop surge, praised Maliki profusely after he confronted the rival Mahdi Army Shia militia in Basra.

A pattern of more selective law enforcement emerged from Maliki over the next few years. He opted to not pay and even arrest members of the Sunni "Sons of Iraq" who fought al-Qaida from 2006-08. His government purged Sunni members of a rival political faction that nevertheless won the 2010 parliamentary election, although Maliki dug in during a subsequent deadlock and ultimately hung on to power.

Hashimi told Foreign Policy magazine that Washington had helped ensure Maliki's grip on power in an ironic confluence of interests with its adversary Tehran. "Iran actively supported Maliki, and we discovered in due course that the US also supported Maliki," the ousted vice-president said in 2011 after fleeing Baghdad.

While US criticism of Maliki was muted, Colin Kahl, the senior Pentagon policy official with the Iraq portfolio, said the government "tried to stay aloof from picking winners or losers" and only backed Maliki "toward the end when he looked inevitable".

This week, one of the US's former "winners", Ahmed Chalabi, has slowly re-emerged as a potential consensus candidate if, as seems increasingly likely, Maliki finds himself adrift. Once a Pentagon favourite, but for the past 10 years a US pariah, Chalabi sat down with the US ambassador to Baghdad this week, according to the New York Times. It is a move that, in such a combustible political climate, is sure to further threaten Maliki's tenure.

The Guardian can confirm that Chalabi, a former deputy prime minister and source of some of the intelligence that led the US to war in Iraq, also met with Suleimani. The stars may be aligning for him. But they are rapidly dimming for Maliki.