WASHINGTON (Reuters) - Over the span of just a few hours, U.S. President Donald Trump upended his own policy on Syria with a chaotic series of pronouncements, blindsiding foreign allies, catching senior Republican supporters off guard and sending aides scrambling to control the damage.

Trump’s decision on Sunday to remove some U.S. forces from northeastern Syria, opening the door to a Turkish offensive against U.S.-allied Kurdish fighters, provides a vivid example of how, with traditional White House structures largely shunted aside and few aides willing to challenge him, he feels freer than ever to make foreign policy on impulse.

While Trump’s erratic ways are nothing new, some people inside and outside of his administration worry that the risk of miscalculation from his seat-of-the-pants approach may only increase as he moves into re-election campaign mode facing other unresolved, volatile international issues such as Iran, North Korea and Afghanistan.

He also made clear on Monday that he was determined to make good on his 2016 campaign promise to extract the United States from “these endless wars,” although his plans for doing so are clouded by uncertainty.

It comes as Trump is under growing pressure from a Democratic-led impeachment inquiry over his efforts to get Ukraine to investigate one of his political opponents, former Vice President Joe Biden.

“There’s a real sense that nobody is going to stop Trump from being Trump at this stage, so everybody should buckle up,” said one U.S. national security official, who cited Trump’s firing last month of national security adviser John Bolton as a sign of the president being less restrained than ever by his top advisers.

Trump’s policy whiplash on Syria started shortly after a phone call with Turkish President Tayyip Erdogan on Sunday in which he sought U.S. support for Ankara’s planned incursion.

Several hours later, the White House issued a late-night statement - which, according to one administration official, was dictated directly by Trump to a senior aide - that said U.S. forces “will no longer be in the immediate area.”

This suggested that Turkey could be given free rein to strike Kurdish forces long aligned with Washington in the fight against Islamic State.

Trump, in a series of Monday tweets, appeared to double down on plans for a U.S. troop drawdown if not a full withdrawal, but later threatened to destroy the economy of NATO ally Turkey if it took its military operation too far. That seemed to be an attempt to placate criticism, including from Republican Senate Majority Leader Mitch McConnell, that he was abandoning the Syrian Kurds, who denounced it as a “stab in the back.”

CONFUSION AMONG TRUMP AIDES

The latest presidential pronouncements on Syria injected news confusion over U.S. Syria policy.

Last December, acting without a formal policymaking process, Trump called for a complete U.S. withdrawal from Syria. But he ultimately reversed himself after drawing strong pushback from the Pentagon, including the resignation of then-Defense Secretary Jim Mattis, and an uproar on Capitol Hill and among U.S. allies in Europe and the Middle East.

Trump insisted to reporters on Monday that he “consulted with everybody” on his new Syria decision, although the announcement seemed to catch Congress as well as some within his administration by surprise.

“He makes impulsive decisions with no knowledge or deliberation,” tweeted Brett McGurk, who served as Trump’s envoy for the international coalition to combat Islamic State and quit after the December Syria policy uproar.

Trump’s abrupt decision on Syria came after learning in the phone call with Erdogan that the Turks planned to go ahead with a long-threatened incursion, a senior administration official said.

“We were not asked to remove our troops. The president when he learned about the potential Turkish invasion, knowing that we have 50 special operations troops in the region, made the decision to protect those troops” by pulling them back, the official said.

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The official underscored that Trump’s decision did not constitute a U.S. withdrawal from Syria.

Trump made clear to Erdogan that the United States did not support the Turkish military plan, which came as a surprise to the Turkish leader, a senior State Department official said.

There was some confusion among senior officials trying tofigure out what Trump had actually decided, a source familiar with the internal deliberations at the White House said.

But the senior administration official, speaking on a conference call with reporters, denied that Pentagon officials were “blindsided” and Trump said he had consulted with the Joint Chiefs of Staff.

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On Tuesday, after U.S. forces began pulling back from the Turkey-Syria border, Trump was still trying to clean up after himself. In a morning tweet-storm, he denied abandoning Kurdish forces, the most effective U.S. partners in fighting Islamic State in Syria. But he also praised Turkey as a trade partner, softening the economic threats he had issued the day before.

PROMISED TO BRING TROOPS HOME

U.S. officials told Reuters repeatedly ahead of Trump’s decision that U.S. personnel would not be able to stay in northeast Syria if their Kurdish-led partners, the Syrian Democratic Forces, were forced to turn their attention to a massive Turkish invasion. That view was reaffirmed on Monday, as officials warned that only a limited pullback was expected for now – but a larger one could follow.

“If it’s wide-scale conflict, we would not have a partner in northeast Syria,” one U.S. official said on Monday, speaking on condition of anonymity.

The president saw his decision in the context of fulfilling a campaign promise to ultimately bring U.S. troops home. He visited Walter Reed Medical Center on Friday and awarded Purple Heart medals to a half-dozen wounded warriors.

Trump himself got into the subject earlier when taking questions from reporters at the White House. He said the United States had become a “police force” in Syria and elsewhere in the Middle East and he wanted to change that.

“I have to sign letters often to parents of young soldiers that were killed and it’s the hardest thing I have to do. I hate it,” Trump said.

Some independent analysts said, however, that Trump’s freewheeling way of making war-related decisions could further undermine U.S. credibility with allies and partners. He has already whipsawed on plans for a withdrawal from the long-running war in Afghanistan.

“We find ourselves involved in counterterror operations around the world,” said Fred Hof, a former Pentagon and State Department official. “Potential partners will be looking at what happened in Syria and drawing certain conclusions.”