As world leaders gather this week for the U.N. General Assembly, President Trump has an opportunity to reverse a failed policy in the Middle East and deliver a blow to a terrorist organization by stopping the shipment of arms to the People’s Protection Units, or YPG, the Syrian arm of an organization designated as terrorists by authorities in the United States and Europe.

The U.S. intelligence community has labeled the YPG the “Syrian militia” of the Kurdistan Workers’ Party (PKK), which has waged a violent campaign of terrorism inside Turkey, killing thousands of innocent people. As we repeatedly warned would happen, U.S. support for the group has already backfired. An American Marine was reportedly shot this year by a member of the largest Syrian militia, spearheaded by the YPG. Human Rights Watch has called on the YPG to stop its recruitment of child soldiers.

Recent reports suggest that YPG forces have recently forged an alliance with Syrian President Bashar al-Assad to help him recapture the last rebel stronghold in Syria. An attack by the regime in Damascus would have triggered the worst humanitarian disaster in the violent history of the Syrian war. To head off the conflict, last week Turkey succeeded in negotiating with Russia to establish a buffer zone.

The YPG has been amassing power and territory in Syria just miles from Turkey’s border. Washington has used 5,000 trucks and 2,000 cargo planes to deliver weapons to the YPG in recent years, according to estimates by Turkish authorities. A similar deployment on the borders of any NATO member state would be cause for outrage. This is a fundamental breach of everything for which NATO stands.

Alarmingly, the group has applied to establish a lobbying office in Washington. Its political arm, known as the U.S. Mission of the Syrian Democratic Council, has stepped up its lobbying for more arms and aid, which will be paid for by U.S. taxpayer dollars. The political arm of a terrorist group seeking to peddle influence in Washington is a shocking state of affairs, and President Trump should block its activity.

I’m an ally of the Kurdish people. In fact, my party has been honored to receive notable electoral support among Turkish Kurds. I am, however, a sworn enemy of terrorists of all stripes. I don’t make exceptions. I’m also a student of history. As with the arming of the mujahideen in Afghanistan, once weapons and training are supplied, the trigger is no longer in American hands.

The U.S. administration has presented guarantees that these weapons will not be turned against Turkey. But Syria is in the middle of a war. Realistically, the decision-makers in Washington are in no position to make such promises.

Arming the YPG directly endangers Turkey and its people, who have already faced decades of fear and violence at the hands of a ruthless and radical terrorist movement. And now, with the help of our NATO ally, the PKK is being armed to the teeth. Turkey sounds the alarm because unless drastic, immediate steps are taken to reverse course, our citizens will suffer as a result of this reckless policy.

Every day, Turkish security forces work hard to prevent DEASH fighters from fleeing Syria and travel through Turkey to Western capitals. Our military and intelligence forces work closely with the United States and other allies to track and arrest terrorists, avert attacks and gather critical information.

This work has put a bullseye on Turkey’s back — and my own — from DEASH and other extremist groups. They know our resolve and commitment will not waver, which is why they’ve attacked our shopping malls, airports and other major civilian targets. But we have kept up the fight with raids, locking them up, foiling their plots and preventing their passage.

Our ultimate mission — protecting our people from harm — is sacrosanct. Turkey is proud that our actions save not only Turkish but American lives. And it’s because of those lives saved, because of the burden we’ve shouldered in the interest of our collective global security, that Turkey is right to insist that the United States not arm terrorists who are dedicated to our destruction.

It’s time to choose a side.