There can be no doubt that U.S. President Donald Trump's decision to withdraw from Syria plays into Iran's hands. Ever since the 1990s, the Iranians have seen the United States as presenting the greatest threat. Accordingly, and with the aim of achieving regional hegemony, the primary objective of Iran's strategy has been to limit the U.S.'s presence and influence in the Middle East. In the past two years, Iran was increasingly concerned by Trump's policy on Tehran, which included Washington's withdrawal from the nuclear deal and the imposition of severe sanctions on the ayatollah regime. These steps, along with Trump's unpredictable behavior, helped bolster American deterrence against Iran. The U.S. presence in Syria was beneficial to Israel and reflected Washington's willingness to help Jerusalem out.
The decision to withdraw from Syria could negatively impact American deterrence against Iran because it portrays the U.S. as the one who has been deterred from using force. The U.S. could be seen as willing to limit its role in the Middle East and undermine the security of its allies. Iran could, as a result, become convinced it has been afforded new opportunities to promote its interests in the region, in particular in Syria and Iraq.
Above all else, Iran could respond to the U.S. move by deciding to bolster its efforts to maintain forces and aides in Syria in the long-term. In recent months, the future of these forces had been in question for a number of reasons, including that the Iranians have no good military answer to Israeli strikes and the U.S. has demanded their removal from the area. Russia is also liable to act to end or limit their activities, possibly through a deal with the United States, in an effort to prevent an all-out confrontation between Israel and Iran that will endanger Syria's rehabilitation. Now, the withdrawal of U.S. troops could make it even more difficult to exert military pressure on Iran.
Another development concerns the Iranian plan to establish a land corridor that stretches from Iran to Syria and Lebanon and passes through Iraq. The purpose of this corridor is to transfer weapons and members of the Revolutionary Guards and Shiite militia, in particular, Hezbollah. But the land corridor plan went partially awry as a result of Israeli airstrikes on Iranian targets inside Syria and Islamic State activity in the area as well as concerns the U.S. military presence in the border area between Iraq, Syria and Jordan would disrupt its implementation. Although a few small convoys have apparently passed through the corridor, the Iranians have in large part preferred to move freight by air. With the Americans' inevitable departure, the Iranians will be less concerned about the possible disruption of traffic through the corridor and will likely decide to expand their use of the corridor.
And yet despite all this, the change will not likely be so far-reaching. The American attacks on Iranian forces and Shiite militias in Syria and Iraq were carried out on a small scale and relatively rare. Almost all of the air strikes on Iranian targets in Syria were carried out by the Israeli Air Force, who exposed the Iranian military's weaknesses and made it difficult for Tehran to establish a military outpost in Syria. Israel has already declared it intends to continue to strike Iranian targets in Syria as necessary to prevent their establishment in the country, and rightfully so.
Even with the troop withdrawal, the U.S. administration can continue to assist Israel in thwarting the establishment of an Iranian front in Syria. The White House still has a negative view of Iran and can act to increase pressure on Tehran. Despite now having fewer tools at its disposal, Washington can also try to convince Russia not to assist the Iranians in fending off the Israeli attacks and possibly lead to the eventual removal of their forces from Syria.
