James P. Cain was U.S. ambassador to Denmark from 2005 to 2009.

Two weeks ago we awoke to the aroma of strong Arabic coffee, which moments later was served to us by a masked, fatigue-clad freedom fighter with an aged AK-47 slung over his shoulder.

We were in the village of Ain Issa, a Syrian hamlet of a few thousand Kurds, Arabs and Christians 15 miles from the front where Russian and Syrian government troops are facing off against forces from the U.S.-led coalition. The AK-47 was there not to threaten but to guard us. We were there to discuss American private-sector investment in northeast Syria, the Kurd-dominated region east of the Euphrates where the U.S.-led coalition has partnered with local forces to push out the Islamic State. Two years ago, a map of the Islamic State’s “caliphate” would have shown most of this area under their control.

Our small group was likely the last private-sector delegation to visit officials in this region before President Trump’s decision on Wednesday to summarily withdraw American troops.

The morning before, in the town of Qamishli, which we had passed through on the way to Ain Issa, an Islamic State fighter had thrown a grenade that killed a young soldier of the Syrian Democratic Forces (SDF), our local allies. Along the way from Qamishli to Ain Issa we saw numerous Islamic State holdouts that had been destroyed by coalition air power. In Ain Issa (which locals translate as “Spring of Jesus”), the buildings where we spent the night were pockmarked and bombed-out.

In Ain Issa, we met with senior officials of the local administration established by the Syrian Democratic Council, the political wing of the Syrian Democratic Forces, to govern the area. (In their demonstration of inclusiveness and empowerment, the SDC has committed to having male and female co-presidents of each of its regions — a contrast, if there ever was one, to the Islamic State’s denial of basic human rights to women). These officials were earnest and enthusiastic in their desire for the United States to remain engaged in the region. “We may have worked together to push Daesh out of this region,” Co-President Berivan Xalid said to us, using the Arabic term for the Islamic State, “but the underlying zealotry that led to their rise remains with us, and they will be back in another form, if America leaves.”

These words were a stark personal reminder of what is at stake here, for it was in these lands that Islamic State terrorist Najim Laachraoui received his training before he embarked on a circuitous route to Brussels, where, on the morning of March 22, 2016, he took part in one of two attacks that killed 32 people, including my son-in-law Alexander Pinczowski and Alex’s dear sister Sascha.

The persistent threat of Islamist extremism is not the only threat under which these allies of ours live; and it is not the only American interest at stake here in northeastern Syria.

It is through this region that Iran hopes to construct its direct land route to the Mediterranean Sea, spreading its repressive fundamentalist ideology along the way. It is this region that Turkish President Recep Tayyip Erdogan has already threatened to invade in order to combat our Kurdish allies. And it is this region that produced more than 60 percent of Syria’s oil prior to the civil war, used by the Assad regime in Damascus to fund its machine of repression and leaving this region virtually destitute. That is why the Russians, allied with Assad’s henchmen, are massed on the banks of the Euphrates, waiting to invade as soon as they perceive any opening in our defenses, as they tried to do in February at Deir al-Zour, only to be met with coalition resistance.

Trump’s decision on Wednesday will give the Russians and the Assad regime just such an opportunity, although they will likely be racing against the Turks and the Iranians, who also covet their share of control over the region. But more threateningly, it will remove the primary barrier to the eventual resurgence of Islamist extremism in the region, whether under the name of Islamic State or some other one. We have witnessed such shortsightedness before, in President Barack Obama’s decision to withdraw from Iraq in 2011, creating the conditions for the Islamic State’s emergence.

Trump has said repeatedly that the United States has for too long been serving as a global policeman without getting anything for it. This is the United States’ opportunity to “get something” in return for the investment of lives and resources expended to push the Islamic State out of northeast Syria — an opportunity to bring economic vitality to a people who have both the will and the natural resources to accomplish that goal, but who, without our support, will once again be pillaged by Damascus, or Tehran, or Istanbul, or even Moscow. Such an outcome would be a significant blow to U.S. national security interests and will give our adversaries in the Middle East yet one more example of a United States that has chosen to abandon not only its allies but also those principles that have attracted hopeful people around the world for more than 200 years.

I strongly encourage the president to reconsider his decision.

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