The morning after America, Britain and France struck targets in Syria in response to Bashar al-Assad’s use of chemical weapons in Douma, President Donald Trump tweeted “Mission Accomplished!” But what is the mission? The day before the attacks, James Mattis, America’s defence secretary, said he had “never seen refugees as traumatised as coming out of Syria”. Over 5m have fled, yet this year America has accepted just 11. Hitting the regime hard enough to inflict real pain risks conflict with Russia, on which America is imposing new sanctions over Syria, and with Iran. Earlier this month Mr Trump had said he would withdraw American troops from Syria. In announcing the strikes he rejected “an indefinite presence” in the country—while promising to “sustain this response” until Mr Assad stops using chemical weapons. Syria’s despot has slaughtered plenty of people with conventional weapons. Mr Trump’s statements imply that the world will do nothing to stop him.