President Donald Trump announced that he intends to withdraw U.S. troops from Syria. To do so would be to breathe new life into ISIS, hand a win to dictators in Russia, Syria, Turkey and Iran, and sell out one of our best allies in the Middle East. It would also wreck one of Trump’s best foreign policy successes of his presidency.

Back in October 2015, President Obama began a policy of having 2,000 military personnel team up with the Kurdish group the Syrian Democratic Forces (SDF) to destroy ISIS. The plan showed immediate benefits, as both groups tag-teamed ISIS, transforming this terrorist organization from their once huge holdings in Syria and Iraq to a mere shadow of itself.

“We have defeated ISIS in Syria, my only reason for being there during the Trump Presidency,” Trump tweeted. White House Press Secretary Sarah Huckabee Sanders doubled down, claiming that ISIS had been defeated.  It reminded many of George W. Bush’s ill-fated “Mission Accomplished” banner on the U.S. Aircraft Carrier during the Iraq War. But the job’s not done. On Dec. 10, ISIS sympathizer Damon Joseph was arrested along with a woman who was a fan of Dylann Roof. Both were plotting to shoot up a synagogue, as Joseph (who is white) is also a fan of the Pittsburgh synagogue shooter, showing a new ISIS-right-wing terrorist alliance, with Jews as the target.

Also, if someone checked with the Defense Department, they would know that the U.S. soldiers were teaming up with the SDF to attack an ISIS stronghold near Hajin, a city in the Middle Euphrates River Valley. According to the DoD, “the campaign against ISIS is not over.”

There are a lot of reasons that such a withdrawal is the worst idea we’ve had for the Middle East.  It would be a clear win for the Syrian regime, led by President Bashir al-Assad (the one Trump attacked for using chemical weapons against his people), and Assad’s allies, which include the Iranian regime, as well as Russian President Vladimir Putin. Our Middle East presence will be severely weakened.

There’s a reason Senate Republicans are aghast at Trump’s inexplicable decision to flee from Syria. As the near-tragedy at the Toledo synagogue, and the shooting in Strasbourg’s Christmas shopping area have shown, the fight against ISIS is not over. But pulling out our troops and leaving our Kurdish allies against ISIS to be butchered, while allowing several authoritarians to emerge as winners, means that every terror attack by an ISIS member, or sympathizer after our troops leave, will be on Trump’s hands. I pray he’ll reverse the worst idea of his presidency.