President Donald Trump’s reversal on plans to withdraw U.S. forces from Syria came after he was convinced European allies wouldn’t remain on the battlefield without American support, risking a resurgence of Islamic State, according to a senior administration official familiar with the decision.

The U.S. will keep about 400 troops in Syria, split between forces in the northeast and the Al-Tanf base in the south, according to the official, who asked not to be identified discussing internal deliberations. The White House expects the remaining multinational force in Syria to be about 1,500 troops, though European allies haven’t yet signed off on the plan, the official said.

The U.S. won’t be in charge of the coalition’s military operations but it will provide what the official called infrastructure. One goal of the force will be to ensure Turkish troops — who were expected to target America’s Kurdish allies after the U.S. departed — don’t venture further into Syria.

Despite earlier pledges to get American troops out soon, there is no timeline yet for a complete U.S. withdrawal, the official said.

‘Sand and Death’

The reversal in policy shows the risks of Trump’s improvisational approach to foreign affairs. After he made the decision to get out of Syria — which the president has said is nothing but “sand and death” after eight years of civil war — Defense Secretary Jim Mattis quit. There was bipartisan pushback from members of Congress, who worried a pullout would give Islamic State space to rebuild and lead to Turkish attacks on Kurdish allies.

Senator Lindsey Graham, a South Carolina Republican who has advocated maintaining a troop presence in Syria, applauded the president’s decision when it was first announced by the White House on Thursday, saying it would prevent Iran from filling a power vacuum.

“With this decision, President Trump has decided to follow sound military advice,” Graham said. “This decision will ensure that we will not repeat the mistakes of Iraq, in Syria. For a small fraction of the forces we have had in Syria, we can accomplish our national security objectives.”

After the withdrawal was announced in December, Graham said on Twitter that it would be a “boost to ISIS” and a “huge Obama-like mistake.”

Munich Conference

Additional pressure on Trump came from European allies, who rejected American calls that NATO members step up to fill the void in resources and personnel left by the U.S. departure. Vice President Mike Pence found little support for that demand last week at the Munich Security Conference, a key annual event for top foreign policymakers from around the world.

Asked about the U.S. plans for Syria at the conference, Spanish Foreign Minister Josep Borrell bluntly said, “Spain and the majority of countries aren’t prepared to step in for the U.S. after a withdrawal that was decided in a unilateral way, by surprise.”

There had been about 2,000 U.S. troops in Syria when Trump, during a call with Turkish President Recep Tayyip Erdogan in December, surprised his own aides by deciding to pull all forces out, saying the U.S. had achieved its goal of wiping out Islamic State’s so-called caliphate.

Trump later walked that move back, with him and his top aides saying the U.S. would begin a deliberate withdrawal that would allow it to continue targeting Islamic State during and after the pullout. That only raised more questions about American strategy.

The president signed off on the new plan to keep 400 troops in Syria with National Security Adviser John Bolton on Thursday and Bolton then notified officials at the State Department and Pentagon, according to the administration official.

White House Press Secretary Sarah Huckabee Sanders had first announced Thursday night that the U.S. would keep about 200 troops in the country, but another administration official, who asked not to be identified, said that the total didn’t include forces at Al-Tanf, which U.S. and Israeli officials view as important in constraining threats from Iran and the Hezbollah militants it backs.

The new announcement came hours after Trump spoke again by telephone with Erdogan. Immediately after the call, the White House said in a statement that the two leaders had “agreed to continue coordinating on the creation of a potential safe zone.”

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Turkey’s Defense Minister Hulusi Akar was scheduled to meet Acting Defense Secretary Patrick Shanahan at the Pentagon on Friday, where the subject of Syria was expected to be a key focus.