The assassination of former Afghan president Burhanuddin Rabbani last month has deepened the pessimism surrounding Afghanistan’s already stagnating peace process and prospects for future stability. Speculation abounds over who murdered him — the Quetta Shura, the Afghan Taliban organization based in Pakistan; the insurgent Haqqani network, at the direction of its patrons in Pakistan’s intelligence services; or a faction of the insurgency working without official sanction. Rabbani’s assassination follows a number of attacks attributed to Pakistan-sponsored insurgent groups. These incidents have provoked fierce hostility toward Islamabad from both Kabul and Washington, and have raised fears that Afghanistan is lurching toward civil war.

Rabbani led the High Peace Council, a body of 68 Afghan leaders charged by President Hamid Karzai with seeking peace with the Taliban insurgency. Two months ago, we met with Rabbani in his home to discuss his diplomatic efforts. Rabbani insisted that Taliban insurgents wanted to come to the negotiating table but that they were being held back by their Pakistani minders — as witnessed in the high-profile arrest of their deputy commander, Mullah Abdul Ghani Baradar, by Pakistan in February 2010. He also argued that the sources of funding for the Taliban, again from Pakistan, had to dry up for peace to be possible in Afghanistan.

His observations do not explain why Pakistani military officials would escalate attacks on Kabul at this particular time. But they do highlight the Pakistani role in obstructing peace. Despite the fact that Pakistan’s leadership has a clear interest in controlling the shape of the talks and input in the outcome, it continues to resist serious engagement with the U.S. and Afghan governments on political settlement discussions. It has responded only with deflections and denials to public rebukes from U.S. officials regarding its continued support for the Haqqanis and other militant groups attacking in Afghanistan. The conference of political leaders in Islamabad last week and President Asif Ali Zardari’s column Sunday in The Post underscored Pakistan’s perception that it had borne the heaviest costs of U.S. policies, but they offered little suggestion as to a way forward. In private, Pakistani officials appear equally unwilling to articulate a preferred alternative strategy for Afghanistan, a desired end-state or the format of settlement talks over Afghanistan’s future.

Instead, Pakistani engagement in Afghanistan for the past 10 years has taken the form of hedging and spoiling; in the wake of the most recent attacks, the Obama administration has sent a message that its patience with this behavior is running out. It is in both Pakistani and U.S. interests that Islamabad respond to this challenge with a constructive settlement proposal that shows its goals do not lie in the destabilization of its neighbor.

If Pakistan cannot bring insurgent elements to the negotiating table, and present a plan for a political settlement or a desired outcome, the United States will have no choice but to take more aggressive steps. The United States should begin by labeling the Haqqani network a terror group. Other options include cutting all military assistance to Pakistan, and coordinating among international and regional allies to more sharply contain and isolate Pakistan.

But as Rabbani recognized, not all of Afghanistan’s problems stem from Pakistan. Afghans themselves have to work to find a more acceptable political outcome. The country’s political system does not have sufficient support among Afghans, let alone from the Pakistanis. Many Afghans see the Kabul government as exclusive and unaccountable, enriching a small elite. Power is overcentralized in the office of the presidency, with no checks within Afghan institutions or in the broader society to redress wrongs, channel grievances, or determine budgets and policies.

Given the unsustainable status quo, the United States is not going to fight its way to peace, either by destroying the Haqqani network or by escalating war in Pakistan. Without a broader agreement among Afghans and a supporting regional framework that includes Pakistan, it is unlikely the Afghan National Security Forces will hold together, let alone beat back an insurgency that maintains a haven in Pakistan. Success is far from guaranteed, but the pursuit of a political settlement represents the best possible remaining outcome for the U.S. mission in Afghanistan, even if it falls short of a full-scale agreement.

The Obama administration has in recent months rightly renewed an emphasis on a political settlement and regional diplomacy. Rabbani’s assassination and the recent attacks should not derail those efforts. But it should show U.S. policymakers that they must take a stronger role in this process, facilitating inclusion of more stakeholders at all levels of society, pressuring regional powers and addressing their fears, and constructing incentives for Karzai to address Afghan grievances through political reforms. The United States must orient its strategy around facilitating a lasting settlement, rather than getting caught in a cycle of retribution against insurgents and Pakistan.

John Podesta is president of the Center for American Progress. Caroline Wadhams is a senior fellow in the center’s national security program.