As he soberly announced the assault, Mr Trump argued that the move was still within the framework of his 'America First' foreign policy agenda.
The US, he said, has a "vital national security interest" in stopping the proliferation of the kinds of chemical weapons the Syrian government used against its citizens earlier this week.
Yet Mr Trump's actions left no doubt that - at least in this instance - his view of America's role in the world has been altered.
Mr Trump is hardly the first president to reconsider his views after assuming the responsibility of controlling the world's most powerful military.
But with a major shift coming just 77 days into his presidency, his may be one of the fastest transformations in recent memory.
After spending years warning US leaders that Syria was a dangerous quagmire, Mr Trump is said to have been moved by the gripping images of young Syrian children's listless bodies that were beamed across the world following the chemical attack.
He mourned the "beautiful babies" among the dozens killed by the deadly gases and accused Syrian President Bashar Assad of having "choked" his own citizens.
His sentiment - the US's "responsibility to protect" - echoed those often used by some of Mr Trump's most ardent detractors.
The doctrine, espoused most notably by President Barack Obama's former ambassador to the United Nations Samantha Power, holds that world powers have an obligation to defend civilians from conflict, particularly from their own governments.
Mr Trump campaigned on a wholly different vision for the nation's foreign policy, one that bordered on isolationism and centred on recalibrating trade deals with international partners. He has specifically said the Middle East is one region of the world he hoped to avoid.
Yet in the short term, Mr Trump's decision to plunge the US deeper into the Syria conflict won him plaudits from his own party. Even some Democrats were muted in their response, a signal of how frustration with US inaction in Syria has permeated both parties.
"The question now is what the consequences and reactions will be, and what are the president's strategic and long-range goals and plans with respect to US involvement in Syria," said Senator Jack Reed, the leading Democrat on the Armed Services Committee.
Mr Trump's decision was all the more remarkable for his strident public opposition to launching a strike on Syria when the decision weighed on his predecessor. In September 2013, he repeatedly took to Twitter to urge Obama to not to attack Syria after another chemical weapons attack.
"AGAIN, TO OUR VERY FOOLISH LEADER, DO NOT ATTACK SYRIA - IF YOU DO MANY VERY BAD THINGS WILL HAPPEN & FROM THAT FIGHT THE U.S. GETS NOTHING!," he wrote.
He followed two days later with another tweet declaring: "There is no upside and tremendous downside."
President Obama nearly ordered strikes, but ultimately pulled back. He called for a vote in Congress that never came, then rallied behind a Russian-backed plan to remove Syria's chemical weapons stockpiles - an agreement that appeared to have failed, given this most recent attack.
Though Mr Trump castigated Obama for appearing weak and indecisive, he maintained as a candidate that Syria was a morass the US should avoid.
As recently as a week ago, his top diplomats, Secretary of State Rex Tillerson and UN ambassador Nikki Haley, both indicated the US might take a hands-off approach to a civil war that has killed hundreds of thousands of people and forced millions more from their homes.
The long-term implications of Mr Trump's sudden policy shift are uncertain. But his supporters seemed willing to accept his decision.
"President Trump has tonight more than earned a second or third look from a lot of doubters - both at home and abroad," said Kevin Kellems, a Republican strategist.
In addition to the blunt message sent to Assad, the strikes are also a signal to Russia and Iran, Syria's main benefactors, as well as China, which the US believes is not doing enough to stop North Korea's nuclear pursuits.
Mr Trump ordered the attack while hosting Chinese President Xi Jinping at his Mar-a-Lago resort in Florida amid an ongoing struggle between Washington and Beijing over how to rein in Pyongyang's nuclear weapons and ballistic missile programmes.
"This clearly indicates the president is willing to take decisive action when called for," Mr Tillerson said.