Next month marks the 15th anniversary of the beginning of the war in Afghanistan. It has lasted longer than both world wars and the Vietnam War. In fact, it’s the longest in U.S. history. A recent trip to Afghanistan on national security issues convinced me that it will go on even longer. That means not just continuing the fight, but rethinking how we fight.

In July, President Barack Obama decided to slow the pace of U.S. troop withdrawal from Afghanistan. I questioned that decision because the president’s original plan was to reduce the number of troops from 9,800 to 5,500 before he left the White House in January. However, given a deteriorating security climate and resurgent Taliban, he was forced to keep 8,400 U.S. troops on the ground.

My conversations with senior U.S. military officials in Afghanistan helped me put into perspective the president’s decision. After the end of NATO’s combat mission in late 2014, a critical mass of troops withdrew and handed over security responsibilities to Afghan forces. Unfortunately, Afghan troops struggled to contain a burgeoning Taliban that was able to regain some of the territory once controlled by U.S. and NATO forces. At the end of January 2016, more than 70 percent of Afghan districts were under Afghan government control or influence. But by the end of May, that figure had declined nearly 5 percent. Additionally, almost 9 percent of districts were under insurgent control or influence, and 25 percent were at risk of falling to insurgents.

As a result of the president’s decision, the security climate has recently improved. Most notably, the capability of local Afghan security forces has strengthened and helped the government regain control of cities and territories it had lost to the Taliban. The ISIS offshoot, Islamic State Khorasan, no longer shows the ability to wage a sustained fight after Afghan forces pushed them into retreat.

Despite continued U.S. involvement, major uncertainties remain over the future of Afghanistan’s security. Most U.S. ground troops continue to have a very narrow mission, supporting counterterrorism operations and training of local forces. And America’s next president will be responsible for determining whether to expand or contract that role.

Rightly so, 15 years of fighting in Afghanistan has led many Americans to ask whether this war will ever end. While I am not prepared to say that we will remain in Afghanistan for as long as we have kept a presence in Germany, Japan or South Korea, I do believe that we will be fighting terrorist elements there for the foreseeable future.

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To help U.S. troops complete their mission, we must reorganize our military so it emphasizes counterterrorism missions — increasing rapid reaction, mobility and agility, and enhancing our intelligence capabilities. The United States must review old weapons platforms and deploy lighter, more precise technologies that utilize new systems to help troops fight smarter and safer.

After World War II, the United States reorganized its military infrastructure to meet new threats by creating the Department of Defense. We developed the Marshall Plan to aid Western Europe and prevent the world from slipping back into war. And in the 1980s, we passed the Goldwater-Nichols Act to reorganize our military again and develop a more streamlined and efficient chain-of-command across branches. Now, facing a jihadist arc across the Middle East and beyond, the United States must reorganize again, using both hard and soft power. It can’t fight 21st century threats with mid-20th century mindsets.

In this new world, we face enemies who don’t bother with conventional warfare rules. To defeat them, we must consider not only how long we fight, but also how we will fight.

Rep. Steve Israel is retiring from Congress this year.