BY SETH J. FRANTZMAN, OPINION CONTRIBUTOR-The Hill

“We have defeated ISIS in Syria,” President Donald Trump tweeted on Wednesday, and U.S. officials told reporters that U.S. troops and diplomats would be withdrawn soon, to wrap up operations there after several years of supporting the mostly Kurdish Syrian Democratic Forces fighting ISIS. This extraordinary reversal in U.S. policy threw into question the administration’s commitment to its allies on the ground, and potentially could lead to new problems in Syria as Russian, Iranian and Turkish forces fight over the vacuum left by the United States.

Critics of Trump’s decision such as Sen. Lindsey Graham (R-S.C.) predicted ISIS would rebound: “I don’t agree they are defeated in Syria and Iraq,” Graham told Fox News. He argued on Twitter that there would be resentment and feelings of abandonment by U.S. partners. But others, such as Sens. Rand Paul (R-Ky.) and John Barrasso (R-Wyo.), agreed with Trump, saying Americans want to bring the troops home. Yet Barrasso warned that the United States should be wary of allowing Iran and Russia to exploit the situation.

Until the president’s surprise announcement, U.S. officials had said troops would stay in Syria to help stabilize the situation, train forces to secure the area, ensure that ISIS would not come back, and even use eastern Syria to make sure that Iran’s influence was reduced in the country. James Jeffrey, the U.S. special representative for Syria engagement, has been traveling extensively to talk about the future of Syria; he discussed concerns about Iran with Israeli officials, and told the Atlantic Council in mid-December that the United States was working on a political process for the future. Now, many will wonder why administration’s officials were not on the same page as the president.

The battle against ISIS is not over. The United States launched 208 airstrikes between Dec. 9  and Dec. 15, among the highest number of airstrikes in the recent campaign against ISIS. Since August, the number of airstrikes has increased from an average of 1.6 a day to 30 a day in Syria. Although these strikes are mostly confined to a small area of Syria along the Euphrates river near the Iraqi border, there is still ISIS activity in both Iraq and Syria. ISIS is media savvy and will be aware of U.S. statements; its leaders likely will bide their time before beginning another campaign of terror. ISIS thrives in ungoverned spaces of the sort found on the Iraq-Syria border.

A U.S. withdrawal also could embolden a Turkish operation against Kurdish groups in Syria. For weeks, Turkey has warned that it will launch an operation in eastern Syria, which the U.S.-led coalition had called unacceptable. Ankara has accused the Kurdish groups, especially the People’s Protection Units (YPG), of being the Syrian branch of the Kurdistan Workers Party (PKK), and Turkish President Recep Tayyip Erdogan has said that Turkey will not allow a “terror corridor” along the border. Erdogan has vowed the operation will begin soon.

After four years battling ISIS, the YPG now would be dragged into this battle and may need to ask Bashar al-Assad’s government to return troops to eastern Syria to prevent Turkey’s offensive. This could make Russia a broker of a deal, as Russia was when Assad threatened to attack Idlib in northern Syria, where Turkish observers are present. Turkey backs the Syrian rebels, and Russia has been working with Turkey and Iran, which backs the Syrian regime, to discuss a new constitution for Syria. Now, Russia, Iran and Turkey will jockey for control.

Iran’s growing presence in Syria is of great concern to Israel. Iranian foreign minister Javad Zarif tweeted on Wednesday that the West has been compelled to accept the role of Russia, Turkey and Iran in Syria’s future. When the United States withdraws, it’s likely that U.S. adversaries will think they’ve won another round.

Seth J. Frantzman spent three years in Iraq and other countries in the region researching the war on terror and Islamic State. He is executive director of the Middle East Center for Reporting and Analysis. A former assistant professor of American Studies at Al-Quds University, he covers the Middle East for The Jerusalem Post and is a writing fellow at the Middle East Forum. He is writing a book on the state of the region after ISIS.