Over the past two weeks, the political significance of the terror attacks in Mumbai has evolved rapidly. India may have borne the brunt of the violence, but over the longer run Pakistan will remain under the spotlight.

As the Mumbai crisis first unfolded, the apparent confusion and ineffective response of India's security apparatus raised concerns about its capacity to protect its people--including the wealthiest and most privileged--from acts of terrorism. Then, as the post-attack investigation took shape, it became clear that the Mumbai terrorists had trained and organized in Pakistan. The familiar specter of Indo-Pakistani war quickly reared its head, recalling the nuclear standoff of 2001-2002, a crisis triggered by the December 13, 2001 assault on the Indian parliament by Pakistan-based militants.

Each of these concerns--about India's internal security capacity as well as the potential for another Indo-Pakistani nuclear standoff--remains quite real. Both demand immediate and ongoing action from the United States. The Bush administration has already taken useful steps towards mitigating the Indo-Pak crisis by counseling patience in India and pressing for a rapid, serious response from Pakistan. Fortunately, top leaders in New Delhi and Islamabad have voiced a commitment to diplomatic, rather than military, solutions to the crisis. Looking to the future, the United States should expand its counterterror cooperation with India to include more extensive technical assistance, lessons learned from our own homeland security efforts, and intelligence sharing. And, assuming this latest crisis recedes, the incoming administration of President-elect Barack Obama would be well-advised to lend quiet support to the Indo-Pak rapprochement process that has proven remarkably effective since 2003.

But Mumbai is not simply a story of weak Indian security institutions or a replay of past Indo-Pak hostilities. We must now recognize that Mumbai represents a dangerous escalation in what might best be described as the "war for Pakistan": a civil conflict over whether nuclear-armed Pakistan succumbs to extremist, Taliban-like ideologies or gropes its way toward a more moderate, modern path. Even if Pakistan's moderates eventually prevail, this war threatens to destabilize the region, especially neighboring India and Afghanistan. If the war is lost, the consequences will be far worse. Building and sustaining stability in Pakistan must be at the top of the agenda for Obama's national security team.

From a Pakistani perspective, Mumbai had less to do with taking India's financial capital down a peg, and more to do with creating regional and international tensions that would distract Pakistan's security forces from their own homegrown insurgency and undermine civilian leaders already overburdened by economic crises and opposition politicking. In short, Pakistan's militants cleverly sought to leverage outside pressure from India and the United States in a bid to squeeze their own state.

But the terrorists have not yet succeeded. Mumbai could, and should, represent a decisive turning point in the war for Pakistan. Islamabad's political and military leadership must now act to take down the militant group Lashkar-e-Taiba (LeT), which apparently organized and perpetrated the attacks and has, over decades, constructed an influential network of operatives and sympathizers throughout Pakistan. Despite having officially banned the organization in 2002, Pakistan's government has never attempted a full and unequivocal effort to dismantle the group.

More than any other group, LeT encapsulates the complicated history of intertwined relations between Pakistani security services and ideologically driven militants. Long nurtured by the state as a means to project influence into Afghanistan and Kashmir, LeT gradually outgrew the control of its sponsors. After 9/11 and the 2001-2002 standoff with India, Pakistan's military leadership started to recognize that the use of proxy fighters like LeT was no longer a sustainable approach to pursuing a Kashmir settlement. But even as the regime of former President Pervez Musharraf decided to shift away from fomenting violence on the Indian side of the Line of Control, it was unable--some believe unwilling--to decommission completely the apparatus of militancy.

Today, Pakistan's leaders may still fear that any concentrated effort to do away with LeT and its associates (including the charitable wing of the party, Jamaat-ud-Dawa, or JuD) risks a backlash of violence and instability that would dwarf the unprecedented carnage of suicide bombings, assassinations, and kidnappings that Pakistanis have experienced over the past year. After all, thousands of LeT operatives have benefited from years of training in the tactics of insurgency. President Asif Ali Zardari also recognizes that a crackdown taken under Indian duress offers an opening to opposition politicians, especially rival Nawaz Sharif, to win public support by sounding hawkish, nationalist themes and portraying the ruling government as weak or cowardly.

For these reasons, Islamabad's current government and top army brass may prefer a gradualist approach to fighting LeT/JuD. The first steps in this approach may be under way: This past weekend, Pakistani security forces raided a LeT compound and apparently arrested one of the main Mumbai organizers, Zaki ur-Rehman Lakhvi. In the coming months, Islamabad may choose to pursue subtle efforts to co-opt, bribe, and reorient members of the LeT organization rather than risk an outright declaration of war. Since JuD has garnered considerable public support for its charity work, avoiding an open fight might also avoid the alienation and radicalization of segments of the Pakistani population who now have no cause for violence.

But there are many problems with taking the slow road against LeT. First, gradualism may not be enough to satisfy a skeptical and angry Indian public, jaded by decades of Pakistan's sham "crackdowns" on terrorists based in its territory. As long as Pakistan is perceived to be avoiding serious action, tensions with India will remain high. These tensions will invariably distract Pakistan's political and military leadership from other pressing issues, including the national economic crisis and ongoing counterinsurgency operations in Bajaur Agency along the border with Afghanistan.

Second, a gradual approach sends a mixed message to Pakistanis, both those opposed to the government and those who might ultimately rally to its cause. Extremists will continue to exploit the apparent passivity of security forces, while moderates will not risk their lives to stand alongside an uncertain government partner. Decades of veiled support to militants in Afghanistan and Kashmir have taught Pakistanis to read between the lines when their government claims to have cut ties with these organizations. So even if President Zardari is serious about driving LeT/JuD out of business over time, persistent skepticism about whether his government has really changed its ways will discourage aggressive action by law enforcement officers on the front lines.

Even though a decisive break with LeT/JuD runs the risk of escalating violence and political instability, it is the only way for Islamabad to demonstrate seriously its intention to cut ties with terrorists and stand firmly against extremism. Should President Zardari and army chief Ashfaq Pervez Kiyani choose to go down this dangerous path, Washington--whether the outgoing Bush team or the incoming Obama administration--should make clear its intention to back Pakistan's leaders to the hilt.

Just as the United States crafted an assistance package intended to help counter militancy along Pakistan's border with Afghanistan, it should consider ways to facilitate Pakistan's crackdown on groups like LeT/JuD that are based outside the tribal belt. In the near term, this effort will necessarily be led by Pakistani military units, intelligence officers, and police. To the extent that the United States can provide technical expertise, equipment, and intelligence to support the effort, it should do so. Diplomatically, Washington should press other states with influence in Pakistan to lend their support. Saudi Arabia's political influence with Nawaz Sharif may be especially vital, since Sharif's party holds power in Punjab's provincial assembly and will be involved in law enforcement efforts throughout the province. Chinese backing could help to sway wavering officers in Pakistan's army, an institution that depends upon Chinese weapon systems and views Beijing as its historical protector.

Working with and through Pakistan to advance the U.S. counterinsurgency/terror agenda in Afghanistan and to facilitate India's emergence as a rising, democratic power in Asia is bound to be slow, costly, and frequently frustrating, but there are no other realistic options. Pakistan's terrorists cannot be contained; they have already demonstrated a sophisticated capacity to exploit the porous land and sea borders of the region. They will not be easily deterred by threats of U.S. military retaliation; some claim not to fear death, while others perceive the post-9/11 longevity of al-Qaeda and Taliban leadership as proof of American weakness. And they cannot be picked off by purely military means. Recent successes from U.S. air strikes against militant compounds along the Afghan border should not be overstated; they are primarily tactics of disruption, unsuited to the goal of uprooting entrenched terrorist networks that extend throughout the Pakistani state.

In the coming months and years, an enhanced U.S. commitment to economic development, education, and health care could target areas now under the influence of JuD and other extremist operations. Vice President-elect Joseph R. Biden, Jr. has long championed a plan to ramp up nonmilitary assistance to Pakistan, and Obama's national security team would be well-advised to follow through on that commitment. At present, however, the United States lacks the institutional capacity to implement sophisticated, targeted development programs in Pakistan. Any increased levels of assistance programming must be complemented by a significant expansion of USAID and State Department officers based in Pakistan and supported by additional staff in Washington. The Pakistan mission is difficult, owing to poor security conditions throughout the country, so incoming U.S. officials will require an unusual degree of flexibility and logistical support in order to formulate and monitor programming. New procedures, training, and personnel suited to the operating environment will be needed.

In the end, Mumbai serves as a timely reminder that Pakistan's terrorism problem is not confined to the Pashtun badlands bordering Afghanistan. Over decades, extremism and militancy has seeped into the institutions, political culture, and society of the entire country, from its Punjabi heartland to its coastal megacity of Karachi. Winning the war for Pakistan will require an urgent, massive, and sustained effort by the United States in coordination with other international partners and allies in Pakistan.