Tony Badran

Opinion contributor

The Trump administration announced Wednesday that all 2,000 U.S. troops in Syria will start returning home very soon. President Donald Trump, who had long expressed his discomfort with an extended military deployment in Syria, explained his decision in a tweet: “We have defeated ISIS in Syria, my only reason for being there during the Trump Presidency.”

The decision carries implications for the administration’s Iran policy, as Tehran and its client, the Assad regime, are poised to take advantage of the American withdrawal. In September, Trump’s National Security Adviser, John Bolton, stated the U.S. would not leave Syria “as long as Iranian troops are outside Iranian borders, and that includes Iranian proxies and militias.” The sudden reversal of this declared policy could have serious consequences for U.S. strategy in the region.

The Iranians have been working to establish a so-called “land bridge” or territorial continuum stretching from Tehran to the Mediterranean via Iraq and Syria. At present, the U.S.-controlled zone in eastern Syria poses a major obstacle to this objective. Already, Iranian-led Shiite militias are operating at the edges of the U.S. zone and could move in swiftly and connect the Iraqi and Syrian terrains. This would provide Iran with overland routes to deliver advanced weapons to Hezbollah in Lebanon, while building up offensive capabilities in Syria, including in the south, along the country’s border with Israel.

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In his remarks announcing America’s withdrawal from the Iran nuclear deal in May, Trump confirmed his administration would work to “block [Iran’s] menacing activity across the Middle East.” In April, the president spoke of not wanting “to give Iran open season to the Mediterranean.” It’s unclear what steps the administration now intends to take to make good on this stated objective. Although the withdrawal from Syria doesn’t eliminate all U.S. options, it does cede critical terrain to Iran.

The withdrawal from Syria will also affect the administration’s economic pressure campaign against Iran and its regional assets. The U.S.-controlled zone in eastern Syria is home to the bulk of the country’s gas and oil fields, currently off limits to Assad. Thus, for years, Iran has been subsidizing its Syrian ally’s energy needs, costing Tehran billions. The Assad regime, with Russian and Iranian support, will now prepare to retake these oil and gas fields.

Stepping out of Syria means others will step in

The vacuum the U.S. withdrawal creates will invite other actors to step in. Turkey, which has long opposed the emergence of an American-protected Kurdish-dominated zone on its southern border, will also look to capitalize on the situation. President Recep Tayyip Erdogan has already threatened to attack key Kurdish-held towns. Fearing a Turkish assault, Kurdish forces likely will look to Russia and Iran for protection. Alternately, Turkey itself could agree to Russian supremacy in the region, provided it keeps the Kurds in check. Either way, the Kurdish forces and regions likely will fold into the Russian-Iranian camp.

The U.S. withdrawal also affects Israel. Since the outbreak of the war in Syria, Israel has been targeting Iranian military infrastructure and advanced weapons systems deployed in Syria and in transit to Hezbollah in Lebanon. Although Israel reportedly has struck Iranian targets in eastern Syria, on the border with Iraq, the presence of a U.S.-controlled zone there mitigated the threat. Israel will have to recalibrate, and possibly intensify its operations in the area, even as it turns its attention to the Iranian threat in Lebanon.

The Trump administration’s withdrawal from the Iran deal and announced campaign of maximum pressure on Tehran were important strategic moves to roll back Iran’s expansion in the Middle East. But a precipitous U.S. withdrawal from Syria — giving Iran’s clients control of Syria’s energy resources and its forces freedom of movement across the region — poses a serious challenge to President Trump’s strategy.

Tony Badran is a research fellow specializing in Syria at the Foundation for Defense of Democracies. Follow him on Twitter: @AcrossTheBay