The Wall Street Journal | Gerald F. Seib: In the tortured history of U.S.-Iranian relations, no American leader has been as intent on making life difficult for Iran as has President Trump. He has exerted economic pressure, diplomatic pressure, even indirect military pressure.









The great paradox of the moment, then, is that�Mr. Trump�s decision�to pull back U.S. troops in Syria actually is making life easier for Iran in a host of ways. As has often been the case in dealing with Iran, American impulses have collided with the Middle East�s harsh law of unintended consequences.

President Trump now is considering leaving�a few American forces in northeastern Syria, largely to keep an eye on the region�s oil fields. He initially ordered them to all leave, clearing the way for Turkish troops to move in and�eliminate the Kurdish fighters�who had been America�s best allies in the fight against Islamic State extremists.

Still, the American retreat remains good news for Iran. For Iran�s leaders, Syria has become the most important spot in their quest to expand their influence in the Middle East, and Syrian leader Bashar al-Assad their most important ally in that quest. The departure of American forces shrinks America�s role and reduces an impediment to both Iranian influence and Mr. Assad�s continuation in power.

Moreover, the U.S. withdrawal also allows for Kurdish fighters, no friends of Iran or the Syrian regime, to be pushed into the margins.

�Iran wants to consolidate Assad�s rule in Syria, reduce America�s presence in the Middle East, and thwart Kurdish autonomy,� says Karim Sadjadpour, an Iran analyst at the Carnegie Endowment for International Peace. �Trump�s decision checked all three of those boxes, and Iran didn�t have to offer anything in return.�







Beyond that, the Syrian retreat has opened the door for a stronger relationship between Iran and Russia, with potentially adverse consequences for the U.S. Mr. Trump has essentially invited Russian leader Vladimir Putin to step into the vacuum the American departure has created�and Mr. Putin seems all too willing to do so.



Mr. Putin appears to have set out to broker a condominium under which Syria, Turkey and Iran, as well as the Kurds, all figure out a way to survive in the tangled politics of Syria.

It�s certainly true that Mr. Putin has taken on a thankless task in trying to untangle that mess, particularly when his interlocutors hardly see eye to eye. Iranian President Hassan Rouhani wants Syria�s Mr. Assad to survive and thrive, while Turkish President Recep Tayyip Erdogan wants him gone.

In any case, though, Mr. Putin has become the man to see about Syria. Just last month, Iran�s Mr. Rouhani and Turkey�s Mr. Erdogan both dutifully trooped in to see him to start trying to work out an understanding.

It�s hard to know how much the newfound chumminess between Iran and Russia will undercut American efforts to get Russia to cooperate in exerting pressure on Iran to abandon its nuclear program, but it can�t be helpful.

On a broader scale, the American decision to abandon its longtime Kurdish partners threatens to sow new doubts among America�s other allies in the region, particularly in Saudi Arabia and Iraq, about how reliable America really is as a friend and protector.



Such doubts also represent good news for Iran, and its plans for regional domination. Iranian leaders devote a lot of energy on muscling their way into Iraqi internal affairs, in a kind of running tug of war with the U.S., to see who can exert the most influence in a country where America has invested heavily in blood and treasure. Simultaneously, Iran is engaged in a lethal struggle for regional dominance with the leaders of Saudi Arabia and other Persian Gulf states.



Will Saudi Arabia and Iraq and others in the region, uncertain of American staying power, now be more inclined to find ways to accommodate Iran?

For his part, Mr. Trump simply doesn�t believe the benefits of an open-ended American troop presence in a place such as Syria is worth the cost. He�s certainly correct that the U.S. has found it far easier to get engaged in the Middle East than to get disengaged.

And many Americans, including many core Trump supporters, share his conviction that it�s time to stop engaging in what the president calls �endless wars� in the region. In this view, the main reason the U.S. got engaged in Syria was to defeat Islamic State, not to contain Iran. If that primary mission has been accomplished, it�s time to exit.

Inevitably, though, pursuing the goal of leaving Syria complicates the main regional goal, which is to contain Iran. The U.S. can exert maximum pressure on Iran, or it can withdraw from the Middle East. It will find it hard to do both.