Surprise attack raises questions on future US policy over Syria
The cruise missiles that crashed down before dawn on a Syrian air base sent a clear message to President Bashar Assad: the use of chemical weapons will be met with US force.
The outcome is less clear: Mr Assad's grip on power is as firm as ever and he has lost little of his ability to carry out more chemical attacks.
US President Donald Trump said the goal of the military action was deterrence. Officials said strikes targeted the Shayrat air base to prevent it from being used to launch attacks like the one this week that killed more than 80 people and provided sickening images of individuals suffering from exposure to a sarin-like nerve gas. The base's airstrips, hangars and ammunition areas were struck.
The US is not at war with Syria. The intervention was limited, giving Mr Assad's military the ability to end it there by changing its behaviour and allowing for Washington to incrementally expand its military action if required.
But the surprise barrage of missiles raises questions about where US Syria policy is headed after Mr Trump's rapid reversal of positions. Just last week, his administration stressed removing Mr Assad from power was no longer a priority and that America's focus was entirely on defeating an Isil insurgency in the north of the country. But on Thursday night, Mr Trump appeared to endorse a new, open-ended commitment to respond to any use by Mr Assad of weapons of mass destruction.
"It is in this vital national security interest of the United States to prevent and deter the spread and use of deadly chemical weapons," Mr Trump said.
Such declarations carry risks. No US officials declared the threat of more chemical weapons eliminated. If Mr Assad isn't deterred, more attacks would mean more scenes of people foaming at the mouth in agony and bodies lying in heaps. The US may have little option but to up the ante militarily.
Navy Captain Jeff Davis, a Pentagon spokesman, said the US was still assessing the result of the 59 Tomahawks it fired, expressing hope that Mr Assad's government learned a lesson. He said it was ultimately "the regime's choice" if more US military action would be needed.
That raises the potential for Mr Assad to suck the US deeper into the Arab country's brutal, six-year civil war. The conflict has killed hundreds of thousands, contributed to the worst refugee crisis since World War II, and shows no end in sight.
Mr Assad's forces are locked in battle with a bitter, if weakening, opposition camp. Under president Barack Obama, the US spent most of the war trying to stay out of the fray.
Engaging the Syrian government as an enemy means Damascus can respond in kind. That creates added danger for US forces on the ground in northern Syria waging a separate war against Isil, and American aircraft targeting extremist groups from Syria's skies. Up to now, despite public complaints, Syria's government and its allies - Russia and Iran - have essentially given the US and its coalition partners a free pass to conduct their counter-terrorism mission.
If Mr Trump is now willing to protect Syrians from chemical attacks, will he feel compelled to shield others from what has been Mr Assad's more pervasive slaughter? Perversely, the US strikes also risk emboldening Mr Assad to use even greater brutality if he senses Washington's intrusion as a threat to his rule.
"One strike against one air base may be enough to deter him from using sarin gas again, but it will not deter his effort to target civilians, target hospitals," said Jennifer Cafarella, a Middle East expert at the Institute for the Study of War.
The US is also in a murky situation now with Mr Assad's two key international backers.
Keen to avoid any accident that would create a confrontation with Moscow, Trump administration officials told its Russian counterparts of the impending attack and warned them to stay away. US officials, meanwhile, said little about Iran, a country that could retaliate against the US and its allies in a variety of ways, from interfering with Persian Gulf shipping to provoking Israel.
But Edward Djerejian, a former US ambassador to Syria said: "By proceeding with this attack, it's a signal to Assad, to the Russians, it's a signal to the Iranians, to Hezbollah and all those supporting Assad's regime that this is not a free playing field. There are limits."