Ever since Islamabad reluctantly joined the U.S. campaign against terrorism in 2001, it has consistently pursued a strategy of running with the hares and hunting with the hounds. To this day, Pakistan's security services continue to support various terrorist and insurgent groups -- such as the Afghan Taliban, the Haqqani network, and Hezb-i-Islami -- that attack Afghan and U.S. forces in Afghanistan, even as Islamabad continues to extract large amounts of aid from Washington. As the July 2011 deadline for beginning the drawdown of U.S. forces in Afghanistan approaches, Pakistan's continued protection of the insurgents will undermine Barack Obama's plans to improve conditions sufficiently in Afghanistan so as to begin an orderly withdrawal.

Yet both the Bush and Obama administrations have tolerated Pakistan's duplicity with regard to counterterrorism, primarily because the country remains the principal artery for transporting U.S. cargo -- food, water, vehicles -- and fuel delivered to Afghanistan. And, as the recent border closings by Pakistani forces have shown, the Obama administration must implement a Plan B that denies Pakistan the ability to hold the coalition at ransom: It must begin by planning to move larger quantities of supplies through the northern distribution network that runs from Georgia through Azerbaijan, to Kazakhstan, and then Uzbekistan to Afghanistan. Although U.S. forces now receive more supplies through this route than they did before, the dependence on Pakistan is still substantial -- and so consequently is Islamabad's capacity for blackmail.

As a complement to increasing reliance on the northern route, U.S. assistance to Pakistan (totaling roughly $18 billion in civilian and military aid since 9/11) should be tacitly conditioned on Islamabad's meeting certain counterterrorism benchmarks. For starters, all transfers of major military equipment to Islamabad should be contingent on Pakistan ceasing support for militant groups that threaten coalition and national forces in Afghanistan. More extreme (and hopefully unnecessary) options would include expanded drone and air-power operations inside Pakistani airspace. Or -- and this is certain to catch Islamabad's attention -- more open support for Indian contributions to Afghan stability.

The most important problem is that suddenly challenging Pakistan after a decade of acquiescence to its mendacity is tantamount to abruptly changing the rules of a game that Washington and Islamabad have gotten used to: It could result in even greater Pakistani obduracy and further support for its jihadi proxies. Although that is certainly an unpalatable possibility, the bitter truth is that the current state of affairs -- in which Washington indefinitely subsidizes Islamabad's sustenance of U.S. enemies -- poses far greater dangers to the United States. The Obama administration must make the difficult choice now and show Islamabad that the rules of the game have changed.