Victoria Nuland is the chief executive of the Center for a New American Security and a former assistant secretary of state for European and Eurasian affairs.

With his decision to withdraw all U.S. forces from Syria, President Trump hands a huge New Year’s gift to President Bashar al-Assad, the Islamic State, the Kremlin and Tehran. He also guarantees the reversal of U.S. military gains there and extinguishes any leverage Secretary of State Mike Pompeo and his special envoy for Syria, James Jeffrey, may have to drive a diplomatic settlement that meets the administration’s own goals of keeping the Islamic State and Iran out. Most important, Trump falls into the same trap that President Barack Obama did when he withdrew all U.S. forces from Iraq in 2011. Trump’s decision virtually ensures that security will disintegrate further, that the Islamic State and Iran will surge again, and that the United States will be compelled to come back into Syria at even greater military cost and in more adverse conditions than if we had stayed.

Everything about this mercurial decision imperils U.S. national interests as defined by Trump himself. First, the Islamic State is far from gone in Syria. Just six months ago, the Pentagon estimated that 20,000 to 30,000 fighters remained active in Syria and Iraq. The Islamic State may no longer control vast swaths of Syrian territory, but its fighters are hiding in ungoverned pockets in the east and in the back alleys of Idlib. As soon as the United States withdraws, the Islamic State will make three moves. It will claim victory over the U.S. infidels, turbocharging a recruiting binge across the Middle East and South Asia. It will pour fresh fighters into eastern Syria. And it will come out of the shadows to retake territory across eastern Syria from the U.S.-supported Syrian Democratic Forces (SDF), which can’t hold Raqqa or any other cleared territory without continued U.S. help.

The Trump administration is planning to withdraw all U.S. troops from Syria immediately. The president tweeted Dec. 19 that the U.S. had defeated ISIS in Syria. (Jason Aldag/The Washington Post)

Iran will also flood the zone the United States is abandoning. Tehran has likely already given orders for some of the tens of thousands of Hezbollah militias it controls in western and southern Syria to turn east. Just three months ago, national security adviser John Bolton pledged that the United States would stay in Syria until every last Iranian fighter had been driven out. With one tweet Wednesday, the president has instead invited Tehran to deepen its military, political and economic grip on this vital piece of the Middle East. In the process, Iran will also gain control of the major oil fields in Deir al-Zour protected by U.S. forces and the SDF, allowing it to self-finance its land grab.

Moscow is celebrating, too. After years of pretending to negotiate a diplomatic solution to the Syria crisis with Washington, Russian President Vladimir Putin can ignore the entreaties of Trump’s envoys because the United States will have no military skin in the game to back its diplomacy. The Kremlin will proceed as it has long planned, consolidating control over the rest of Syria for Assad until 2021 and then rigging an election for a new figurehead. Moscow will be too smart to expand its own ground presence in Syria, and will instead broaden its tacit support for the Iranian-backed militias that already serve as de facto local police forces in western Syria. Maybe it will allow Tehran to split the spoils from the Deir al-Zour oil fields; maybe all that cash will go back to Moscow.

Of course, both the Islamic State and the beleaguered SDF will fight for that territory, too, setting off another cycle of bloodshed and Iranian weapons shipments into Syria. That, in turn, will draw Israel’s concern and kinetic response. Moscow will then paint itself as the peacemaker and the only power capable of cutting strategic deals with Israel, Jordan, Turkey and others. In the process, Putin will have achieved his long-held dream of restoring post-Soviet hegemony in the heart of the Middle East — at least until the Islamic State surges back.

U.S. diplomacy also died another sad death with Trump’s tweet. Special envoy Jeffrey has had some quiet successes in recent months, including helping to de-escalate tensions between Turkey and Russia over Idlib in September. Jeffrey had been poised to take on the job of midwifing a new political path for Syria, anticipating the likely failure of Russian efforts to negotiate a new constitution by Dec. 31. If the United States withdraws, not even Washington’s Syrian friends will participate in a U.S.-led diplomatic push. They’ll be too busy defending themselves from the Islamic State and Iran.

A few thousand tweets ago, Trump criticized his predecessor for leaving Iraq to the Islamic State in 2011, then having to return in force in 2014. The United States currently has 5,200 troops deployed to Iraq and spends $13.6 million-per-day on military operations there. By that measure, the president should consider our 2,000 troops in Syria a bargain, an insurance policy and vital leverage against far worse outcomes for us, for Syria and for the global balance of power.

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