Since Sept. 11, 2001, the overriding goal of U.S. counterterrorism policy has been to prevent the American homeland from being attacked again. By that standard, at least, the U.S. has done well. The global military pursuit of al-Qaeda has decimated the group’s leadership and eroded its ability to conduct mass-casualty strikes. Gains in homeland security and intelligence collection have disrupted many potential plots. Over the last 20 years, roughly 100 Americans have been killed in jihadist attacks of any kind committed on U.S. soil. That’s about the number who die from gun violence every day.

While recognizing this achievement, it’s important to understand two things. First, the country remains at risk of future attacks. Second, of necessity, the strategy of the past 20 years has to change.

The U.S. response to Sept. 11 was guided by the conviction that terrorists should be fought overseas and, where possible, as conventional military opponents. This thinking was partly misconceived, not least because it underestimated the danger of fueling rather than suppressing the hatred that drives terrorist movements. It was also pursued at inordinate cost — most grievously, the lives of some 8,000 U.S. and NATO service members killed in the wars in Iraq and Afghanistan. U.S. military and counterterrorism expenditures since 2001 exceed $5 trillion in constant dollars. At the height of the war on terror, counterterrorism consumed more than 20% of all U.S. discretionary spending. The withdrawal of U.S. troops from Afghanistan reflects public exhaustion with such commitments.

Whether government strategists like it or not, this experience has pushed the U.S. toward a new approach — one that relies less on overseas wars and more on diplomatic, economic and technological tools to limit the terrorist threat. The challenge for the next 20 years is to shape this subtler and more complex strategy to best effect.

The most crucial task is to understand the enemy. Since Sept. 11, the number of jihadist groups designated as foreign terrorist organizations by the State Department has quadrupled. Despite the progress made by the U.S. military and its coalition partners in degrading al-Qaeda and Islamic State, thousands of terrorist fighters continue to operate in Syria, Iraq and Afghanistan. Jihadists have gained footholds in parts of southeast Asia and are proliferating across Africa, where insurgents threaten the stability of countries such as Somalia, Nigeria, Mali and Mozambique. 

Today’s foreign jihadist groups share Osama bin Laden’s willingness to kill innocent people in service of their ideology. Closer cooperation among law-enforcement and intelligence agencies, aggressive surveillance of militants’ communications, and tighter monitoring of their finances have helped to constrain their reach. These efforts must be maintained and improved.

Despite the public’s rejection of “forever wars,” the U.S. will need to maintain military pressure on radical networks. The biggest challenge is in Afghanistan, where the Taliban’s return to power could once again make the country a haven for violent extremists. Without troops and diplomatic personnel on the ground, the U.S. should increase investments in satellite and reconnaissance capabilities to improve the accuracy of drone strikes. It should seek intelligence-sharing agreements with Afghanistan’s neighbors. And Western counterterrorism agencies should explore the possibility of limited cooperation with the new Afghan regime to target Islamic State Khorasan, a rival of the Taliban and al-Qaeda.

Beyond Afghanistan, the military should maintain a presence in the dozens of countries where small counterterrorism units currently work alongside local forces, backed up by U.S. warplanes and drones. Such “medium-footprint” operations are critical to gathering intelligence on al-Qaeda and Islamic State, cost far less than the counterinsurgencies waged in Iraq and Afghanistan, and have the added benefit of helping the U.S. forge ties with regional military powers whose cooperation will be key to containing China’s growing ambitions.

At the same time, the U.S. needs to rebalance its investments in counterterrorism. This means spending smarter, not less. Upgrade government technology to help the intelligence community process data and track emerging threats. Help local governments around the world strengthen law-enforcement responses to terrorism and boost resilience against attacks. In countries where the U.S. and its allies have limited leverage, provide aid to civil-society and humanitarian organizations working to alleviate the conditions that lead to radicalization. Work with private industry to counter terrorist messaging on social media and harden critical infrastructure against cyberattacks. And broaden the scope to include not just teams of well-trained terrorists but also murderous individuals who’ve been radicalized online. The 2016 mass shooting at the Pulse nightclub in Orlando was by far the deadliest jihadist attack in the U.S. since 2001.

Above all, policy makers and the public should be realistic. A strategy that purports to stop every act of terror is bound to fail and will inevitably produce overreaction when it does. Over the past 20 years, the specter of terrorism has consumed government resources and attention voraciously, and cost too many American lives. The risks posed by terrorism are real and urgent. They can’t be eliminated, but over the next 20 years, they can and should be better managed.

Editorials are written by the Bloomberg Opinion editorial board.

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