Washington — Six weeks ago, Turkey was threatening to invade the Kurdish region of northeast Syria. Last Sunday, U.S. and Turkish troops instead conducted their first joint ground patrol of that area, with Kurdish cooperation. Score one for American diplomacy, backed by patient U.S. military power.

President Trump had said last December that he wanted to withdraw a Special Operations task force that had been assisting the Syrian Kurds in fighting the Islamic State. But many months later, part of that U.S. force remains in place, helping stabilize the region at relatively low cost.

“America is playing the role of mediator between us and the Turks,” Gen. Mazloum Abdi, the commander of the Kurdish-led militia known as the Syrian Democratic Forces, told me in a phone interview last weekend, a few hours before the first U.S.-Turkish joint patrol began. “We know that the Americans are addressing Turkish concerns” about border security, he said. In return, the Kurds want “coordination that will be beneficial for all sides.”

To forestall a threatened Turkish invasion, Mazloum agreed on Aug. 7 to a plan developed by U.S. special envoy James Jeffrey for a “safe zone” south of the Turkish border. Mazloum said that his forces have withdrawn from a border strip that ranges from 5 to 14 kilometers, across a swath of northeast Syria. In addition, the SDF has withdrawn its heavy weapons at least 20 kilometers from the border so that they don’t threaten Turkey.

Many complications remain, and like most diplomatic efforts in the Middle East, this one is still a work in progress. Mazloum protests that the Turks have been conducting unilateral surveillance flights with drones and aircraft, endangering coalition forces. The Turks complain that the Kurds are building new fortifications within the zone, which Mazloum told me are simply shelters for Kurdish civilians in case of future attacks.

The United States had hoped to delay the first joint patrol until U.S. and Turkish units had worked together longer, and a local security force that could replace the SDF had been trained. But Turkey wanted to launch the joint operation last Sunday, so forces were apparently moved into the zone from the Manbij area, where similar U.S.-Turkish cooperation has been underway for months.

The deeper impasse is still there, even as U.S. officials work around the edges. Turkey doesn’t like the idea of even indirect contact with Mazloum’s 70,000-person militia, regarding the SDF as controlled by the YPG militia, which it regards as a terrorist group. Even after the first U.S.-Turkish joint patrol of the zone apparently succeeded, Turkish President Recep Tayyip Erdogan thundered that if the SDF doesn’t leave the zone entirely by the end of September, “Turkey has no choice but to set out on its own,” seemingly renewing the invasion threat.

“It seems Turkey’s ally [the U.S.] is after a safe zone in northern Syria not for Turkey but for the terrorist group. We reject such an approach,” Erdogan said.

But despite Erdogan’s rhetoric, and Trump’s insistence last December that he would pull out U.S. troops, the zone has been established and seems to be holding, with continued American military support. “We are hoping that this process will normalize the situation in our area and impact the process” for an overall political settlement in Syria that would eventually draw the northeast into a reorganized Syrian government, Mazloum told me.

What’s striking, talking to Mazloum, is his calm. Flanked by two volcanic personalities, Trump and Erdogan, the Kurdish leader remains a quiet, seemingly emotionless commander. When I asked whether he still trusted the United States after the roller-coaster of Trump’s troop-withdrawal announcements, he answered simply: “We’re still working together.”

— David Ignatius is a columnist for Washington Post Writers Group.