Voters have consistently brought up the topic of “endless wars” and demands to “bring the troops home” to me since I ran for office. It’s not a left-right issue, either: Both sides question our military presence abroad. I could answer the question in a variety of ways. I could discuss the need to promote American values, prevent the Afghan heroin trade, disrupt the influence of Iran, destroy the Islamic State, defend allies such as Israel, etc.

But in the end, I settle on one very simple reason: We go there so that they don’t come here.

It really is that simple. We bring the fight to the enemy so that they don’t bring it to us. There is a common misconception that if we just let them fight their own wars they will leave us alone. This is wildly untrue for two main reasons. First, groups such as the Islamic State will always try to attack the homeland. And second, even if we manage to prevent them from attacking the homeland, we cannot stop the cascade effect of instability and chaos that ensues when the United States leaves a power vacuum.

Let’s expand on these points. The notion that if we just left these regions alone, they would therefore leave us alone, is at best naive. Consider Osama bin Laden. What exactly did we do to make him hate us? We supported his mujahideens’ cause against the Soviets in the 1980s, and we defended his homeland of Saudi Arabia from Iraqi invasion in the 1991 Gulf War. And yet he planned the 9/11 attacks from Afghanistan, precisely the sort of ungoverned territory that the administration now wants to create in Syria. He hated us because he fundamentally hated Western civilization. The Islamic State and Hezbollah are no different.

And what happens when America retreats? What happens when we allow power vacuums to materialize in some of the most dangerous places in the world? Let’s look at recent history. When I was deployed to Iraq in late 2010, the situation seemed stable. The al-Qaeda threat had been mostly subdued, and the Sunni-Shiite civil war somewhat pacified. We still targeted terrorists on a daily basis along with our Iraqi partners, but most were hiding out in Syria (oh, the glory of hindsight). President Barack Obama was planning to fulfill his campaign promise of total troop withdrawal, despite objections from military leadership. While the situation seemed stable, it was obvious to those of us on the ground that it was only stable because the United States was there. The rest of the story is the history of the Islamic State.

The consequences of a premature withdrawal from Syria are fairly easy to predict: First, now that the pressure is off, the Islamic State will regroup. After they dust themselves off from years of fighting and evading U.S. smart bombs, they will begin planning. They will operationalize their hatred of Western civilization and take advantage of our free societies to plan attacks on our citizens. But since we no longer will have a presence for intelligence collection, we’ll lose much of our ability to see it coming. The allies we formerly relied on — the Kurds and the Syrian Democratic Forces — will have little interest in helping us after we abandon them to Syrian President Bashar al-Assad and Turkish President Recep Tayyip Erdogan.

Second, Hezbollah and, by extension, Iran will expand their influence. Iran will obtain its objective of a land route between Lebanon and Iran, severely endangering our ally Israel and possibly forcing an all-out conflict between Israel and Hezbollah on Syrian territory.

And third, the risk of confrontation between Turkey and our erstwhile Kurdish allies increases dramatically. Another humanitarian crisis could ensue, and anyone in the region who ever thought of trusting the United States to have their back will never trust us again. Our ability to create future alliances will disintegrate.

Stay the course, Mr. President. We may have accomplished the territorial defeat of the Islamic State — and you deserve credit for that — but we are lying to the American people if we let them believe that the chaos of the Middle East cannot reach our borders. Send our men and women to face our enemies there, so that our enemies don’t face us here.