Pakistan has stared down an unprecedented outbreak of US fury over its refusal to reign in the Haqqani network, gaining Washington little and teeing relations up for further decline.
When the retiring chief US military officer, once Pakistan's best American friend, accused Pakistani intelligence of involvement in a 19-hour siege on the US embassy in Kabul, it seemed to signal a sharp change in US policy.
In unprecedented condemnation, Admiral Mike Mullen described the Haqqani network as the "veritable arm" of Inter-Services Intelligence (ISI).
"If they keep killing our troops, that would not be something we would just sit idly by and watch," Mullen warned on September 22.
Four days earlier, US ambassador Cameron Munter fired the starting gun on a concerted campaign to escalate pressure significantly on the nuclear-armed power long distrusted for its double dealings with terror groups.
"There is evidence linking the Haqqani network to the Pakistan government. This is something that must stop," he told Radio Pakistan.
Islamabad denies support for the Haqqanis. Privately, security officials concede there are contacts -- vital to securing any future peace in Afghanistan and to safeguarding Pakistan's interests vis-a-vis Indian influence.
But Washington has rowed back, insisting on the importance of the alliance and stopping short, so far, of blacklisting the Haqqanis as a terrorist organisation -- which could classify Pakistan a state sponsor of terror.
So was there really solid intelligence linking the ISI to the embassy attack and other recent Haqqani assaults in Afghanistan?
Did the United States take a calculated decision that exerting significantly more pressure would get Pakistan to better toe the line, then step back?
Or was Mullen, days from stepping down, just at breaking point, infuriated by Pakistani refusal to isolate the Haqqanis and launch an offensive on their leadership base in North Waziristan?
The trouble, US officials say privately, is that they have no secret arsenal up their sleeve with which to force Pakistan's hand.
Congress signalled it could make aid dependent on greater cooperation from Islamabad in fighting the Haqqanis and the CIA could extend drone strikes beyond the semi-autonomous tribal belt.
But sending a large contingent of US special forces into Pakistan to take out Haqqani networks could rupture the alliance and be costly in terms of lives. Bombing campaigns also risk large numbers of civilian casualties.
"US options are limited as we don't want a larger war in south Asia," said Bruce Riedel, a former CIA officer who advised the White House on Afghanistan and Pakistan in 2009 and a fellow at the Brookings Institution think tank.
Pakistan controls the single most important US supply line into landlocked Afghanistan and allows the Americans to fly through its airspace.
It could end military and intelligence cooperation, deny visas, look the other way on attacks on US interests or even shoot down US drones, writes Daniel Markey, a senior fellow at the Council on Foreign Relations.
Those looking for progress say that the Haqqani pressure, and more importantly the US killing of Osama bin Laden that humiliated Pakistan, have seen the military re-evaluate its decades' old policy of nurturing jihadis.
"They have been exposed for their inefficiency, complicity, duplicity," said economics professor S Akbar Zaidi, based in Karachi but who teaches at Columbia University in New York.
"There must have been a rethink. Whether a new policy has been formulated, whether a new track has been chosen, it's too early to say," he said.
Pakistan gave Mullen's remarks a measured response, uniting military and political leaders behind calls for peace at a rare cross-party conference.
"I think they (Pakistan) actually won... It's actually a sign of a maturing diplomatic response," said Zaidi.
One Western senior official in the United States said the administration had been effective in decreasing the reliance on Pakistan for the supply routes.
"It got the Pakistanis' attention in terms of a decreased leverage that they'd have over the US and in terms of decreased revenues also," he said. But Markey paints a bleak future, seeing interests as irreconcilable.
"There's precious little evidence to suggest that the trajectory of the US-Pakistan relations will go anywhere but downhill," he wrote.