A US officer, from the US-led coalition, speaks with a fighter from the Kurdish People's Protection Units near northeastern Syrian Kurdish town of Derik, known as al-Malikiyah in Arabic, on April 25, 2017.

WASHINGTON — The White House on Wednesday struggled both to rationalize and to defend President Donald Trump's surprise announcement that morning that the United States would withdraw its troops from Syria because, as Trump wrote in a tweet, "we have defeated ISIS in Syria."

But while the announcement contained few answers for the public, Congress or the people likely to be affected by the decision, it did accomplish one thing for the president. It changed the news narrative — from one dominated by stories about Trump's failure to secure the $5 billion he promised to get to build a border wall, to one dominated by coverage of what Trump's Syria decision meant for the U.S. and its allies.

Shortly after Trump's 9:30 a.m. ET tweet, White House 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."

Sanders also claimed that after five years, the United States had defeated the Islamic State caliphate. But she added that American "victories over ISIS in Syria do not signal the end of the Global Coalition or its campaign."

While experts widely acknowledge that ISIS has been forced out of much of the territory it initially seized in Syria and Iraq, the timing of Wednesday's announcement caught official Washington completely off guard.

Among those who learned about Trump's decision from reading news reports were top congressional leaders in both parties and senior military brass. In a more traditional administration, these two groups would have almost certainly been consulted ahead of such a momentous military announcement.

And while the Pentagon took pains to downplay the apparent disconnect between the commander in chief and his top generals, on Capitol Hill, members of Congress did not hide their frustration with the White House.

"I've never seen a decision like this since I've been here, in 12 years, where nothing is communicated in advance, and all of a sudden this type of massive decision takes place," said Sen. Bob Corker, R-Tenn., chairman of the Senate Foreign Relations Committee.