AS 2011 CLOSED, the mainstream press was awash with ominous, dark assessments of the state of the relationship between the United States and Pakistan. After a cross-border NATO air strike in November resulted in the deaths of 24 Pakistani soldiers, Pakistan responded forcefully, closing the Af-Pak border to NATO traffic, expelling the U.S. military from an air base inside Pakistan,(1) and boycotting the International Conference on Afghanistan in Bonn, which had been tasked with outlining the next steps for the occupation.

While Pakistan is likely to re-open NATO supply routes imminently, the incident has significantly altered the tactical parameters of the alliance -- after a drone sortie on November 26, for example, the United States called a halt to drone operations for almost two months, in an attempt to assuage domestic outcry inside Pakistan.

We can be forgiven for thinking we have been here before. Not much more than a year earlier, in October 2010, a similar mishap had elicited a similar reaction from Pakistan. More recently, both the Raymond Davis and Osama Bin Laden incidents, in January and May 2011, had been reported as leaving the relationship in tatters.

There has never been a shortage of alarm about the alliance. The U.S. press has routinely berated Pakistan's "duplicity," accusing it of ties to the Afghan insurgency, and of operating on its own agenda in Afghanistan. Always, these charges are given their gravity by earnest, if apocalyptic, concerns that Pakistan's nuclear stockpile will work its way into the wrong hands.

Yet for all the public handwringing and backbiting, the alliance between Pakistan and the United States has endured the duration of the Afghan occupation. Their shrieking and shrilling aside, U.S. policymakers have seen fit to pour money into the Pakistani Army, year after year, making the country one of the highest recipients of Washington's aid behind Egypt and Israel. Transfers amount to approximately eleven billion dollars since 9/11, the majority of it military in nature(2) -- significant numbers, considering that the Pakistani Army's annual budget is no more than five to six billion dollars without it.

What explains this odd, Janus-faced romance? How has the U.S.-Pakistan partnership persisted in the face of such pronounced tension, even hostility?