Updated 4:05 p.m. | President Donald Trump on Wednesday abruptly declared victory against the Islamic State inside Syria and ordered the Pentagon to withdrawal all American military troops from the war-torn country. Lawmakers were blindsided, but senior administration officials claimed there was no reason for their confusion.

The commander in chief’s decision should have been “no surprise” to lawmakers, said a senior administration official who briefed reporters Wednesday afternoon. She declined to discuss whether Trump caught his Cabinet-level or White House national security officials off guard or whether there had been internal discussions prior to Wednesday morning.

But the senior official did contend no one inside the Trump administration was shocked because both candidate and President Trump’s views on the U.S. military effort in Syria have been “known” for some time.

“It was the president’s decision,” the senior official said when asked about recent speeches and remarks by his national security advisers stating a U.S. withdrawal would be unwise. “The president had made a decision, so previous statements are…”

The official’s voice trailed off, before she added: “He gets to do that. … That’s his prerogative.”

“We have defeated ISIS in Syria, my only reason for being there during the Trump Presidency,” he wrote in a morning tweet. Officials later confirmed reports about his order to remove all U.S. troops.

We have defeated ISIS in Syria, my only reason for being there during the Trump Presidency.

— Donald J. Trump (@realDonaldTrump) December 19, 2018

The move received bipartisan shock and scorn.

Some Republicans in Congress responded with dismay. Sen. Lindsey Graham said in a statement that pulling out troops would be an “Obama-like” mistake that would help terrorists in Syria, strengthen the rulers of Syria and Iran, and abandon Kurds who have joined Americans in the fight against the Islamic State.

Another Armed Services member, Sen. Ben Sasse of Nebraska, also expressed dismay.

“Eight days ago the administration called a hypothetical pullout ‘reckless,’” he said in a statement. “Today, we’re leaving. The president’s generals have no idea where this weak decision came from: They believe the high-fiving winners today are Iran, ISIS, and Hezbollah. The losers are Israel, humanitarian victims, and U.S. intelligence gathering. A lot of American allies will be slaughtered if this retreat is implemented.”

New York Democratic Rep. Eliot Engel, the incoming chairman of the House Foreign Affairs Committee, called Trump’s decision a “precipitous withdrawal” that “leaves scores of unanswered questions.” Atop his list: “How the administration plans to ensure the defeat of ISIS.”

“This move also totally cedes influence to America’s adversaries. Russia and Iran are seeking greater influence in Syria,” Engel said in a statement. “Yet, the United States has no diplomatic presence in Syria. … What is the administration’s strategy for countering our adversaries?”

The president has long been frustrated with the U.S. operation in Syria and the Middle East. As a presidential candidate, he railed against America’s post-9/11 military operations there.

He has argued the billions spent in the region would have been better used at home to upgrade America’s roads, bridges, airports, tunnels, seaports and other infrastructure.

The administration has yet to formally announce a detailed withdrawal plan or final exit date.

“It’s not that I’m not telling you, it’s that I don’t know, quite frankly,” the senior administration official admitted. She referred reporters to the Pentagon, which has been referring reporters to the White House for specifics.

After Trump declared victory over the Islamic State inside Syria in the morning tweet, his top spokeswoman said the broader U.S. and coalition fight against the violent extremist group is not over.

“These victories over ISIS in Syria do not signal the end of the Global Coalition or its campaign,” Press Secretary Sarah Huckabee Sanders said in a statement.

“We have started returning United States troops home as we transition to the next phase of this campaign,” she said. “The United States and our allies stand ready to re-engage at all levels to defend American interests whenever necessary, and we will continue to work together to deny radical Islamist terrorists territory, funding, support, and any means of infiltrating our borders.”

Pentagon spokeswoman Dana White followed with a statement Wednesday afternoon confirming that the process of withdrawing U.S. troops from Syria has begun.

“The Coalition has liberated the ISIS-held territory, but the campaign against ISIS is not over,” White said. “We have started the process of returning U.S. troops home from Syria as we transition to the next phase of the campaign. For force protection and operational security reasons we will not provide further details. We will continue working with our partners and allies to defeat ISIS wherever it operates.”

Removing U.S. troops likely will give Russia and its president, Vladimir Putin, even more sway inside Syria and the region. Trump has been criticized of being too soft on Putin — even amid Justice Department and congressional investigations of his 2016 campaign and possible ties to Russians.

John M. Donnelly contributed to this report.