US President Obama's plan for fighting Isis (Islamic State) is predicated on having a credible and effective Iraqi ally on the ground in Prime Minister Haider al-Abadi.
And in recent days, the Administration had been optimistic, despite the growing political unrest in Baghdad, about that critical partnership.
But that optimism - along with the Administration's strategy for battling Isis in Iraq - was thrown into severe doubt after protesters stormed Iraq's Parliament and a state of emergency was declared in Baghdad.
The big question for White House officials is what happens if Abadi - a critical linchpin in the fight against Isis - does not survive the turmoil that has swept over the Iraqi capital.
The chaos in the Iraqi capital comes hours after a visit by US Vice-President Joe Biden that was intended to help calm the political unrest and keep the battle against Isis on track.
As Biden's plane was approaching Baghdad on Friday, a senior Administration official described the Vice-President's visit - which was shrouded in secrecy prior to his arrival - as a "symbol of how much faith we have in Prime Minister Abadi".
After 10 hours on the ground in Baghdad and Irbil, Biden was hurtling towards his next stop in Rome.
The feeling among Biden and his advisers was that Iraqi politics were on a trajectory to greater calm and that the battle against Isis would now proceed more effectively.
Some hopeful advisers on Biden's plane even suggested that Abadi might emerge from the political crisis stronger for having survived it.
No one is talking that way now.
"There's a realisation that the Government, as it's currently structured, can't hold," said Doug Ollivant, a former military planner in Baghdad and senior fellow at the New America Foundation. "It's just not clear how the Iraqis get out of this. I just don't see how they will."
It is equally unclear how the Administration will move forward if Abadi is unable to consolidate his tenuous grip on power.
For much of the last year, the Iraqi Prime Minister's survival was taken as a given by senior White House officials who were far more focused on the military fight against Isis.
The president and his top aides have pointed to battlefield gains against the group in Iraq as proof that the Administration's much-criticised strategy was working. In the last 18 months, Isis has lost more than 40 per cent of its territory in Iraq, according to US officials.
Attacks on the group's banks in Mosul have blown up cash totaling from US$300 million to US$800 million, according to Pentagon estimates.
"Militarily, the momentum is clearly in the coalition's favour against [Isis]," said a senior Administration official traveling with Biden to Baghdad. "Every objective fact speaks to the fact that [Isis] is losing."
Obama has sought to accelerate the military campaign by sending more than 200 US military advisers to Iraq and giving commanders authority to use lethal Apache attack helicopters in support of Iraqi forces.
In a recent interview, the President said that by the end of the year he expected that the US and its Iraqi partners will have "created the conditions whereby Mosul will eventually fall".
The political crisis in Baghdad began when Abadi made a bold push to replace politically connected members of his cabinet with technocrats and reformers. The Prime Minister said that his moves were intended to stamp out corruption.
But the proposals alienated powerful blocs and provoked raucous debates within the Iraqi Parliament.
Analysts said that the Obama Administration's campaign against Isis was, from the outset, too dependent on Abadi, a weak Prime Minister who is trying to survive in a political system overrun by cronyism and competing sects.
"We get seized with individual personalities," said Ali Khedery, who served as special assistant to five US ambassadors in Baghdad from 2003 to 2009. "We fall in love with them. I agree that Abadi is generally speaking a good ally of the United States, but there isn't much under his control."
Because Iraqi society is so fractured along ethnic and sectarian lines, Khedery said the Administration should adopt a more decentralised approach, working directly with individual Sunni, Shiite and Kurdish leaders.
"What you have is a society that is deeply polarised between communities and even polarised within those communities," Khedery said. "We need a radical new formula."
There is no indication at the moment that the White House is considering such a radical change in approach. For now, the hope is that the current unrest in Baghdad is just a blip.
The protests were sparked by Shia cleric Moqtada al-Sadr, who is now under pressure from Iran and his fellow Shias to rein in the demonstrations, said a senior US official.
"Maybe [Sadr] will realise he took a step too far and will dial it back," the official said. "That could give Abadi more space."
It is also possible that the protests, spurred by the Iraqi Government's failure to provide basic services such as clean water and electricity, could grow worse in the coming days and weeks.
"Iraq is becoming increasingly ungovernable," said Emma Sky, who served as a senior political adviser to the US military prior to the withdrawal of US troops in 2011. "Non-state actors are stronger than the state. The Government is paralysed and corrupt."