WASHINGTON — On the morning after, President Trump declared success. The surgical strike against chemical weapons facilities in Syria had been executed perfectly, he said on Saturday. “Mission Accomplished!” he wrote on Twitter.

That’s a phrase presidents and politicians have studiously avoided since President George W. Bush’s ill-fated aircraft carrier visit prematurely declaring success in the Iraq war. But aside from the curious choice of words, it raised the essential question regarding Syria going beyond the one-time strike: What exactly is the mission?

For most of Mr. Trump’s presidency, it has been to defeat the Islamic State and then get out. But what Mr. Trump outlined in his televised speech to the nation on Friday night was something more complicated. He promised a sustained campaign to stop Syria’s government from again using chemical weapons on its own people, while also emphasizing the limits of America’s ability or willingness to do more to stop the broader bloodletting that has devastated that country for seven years.

Mr. Trump finds himself in a position not all that different from that of his predecessor, President Barack Obama, and with no easier answers. The strike brought home Mr. Trump’s competing impulses when it comes to Syria — on the one hand, his manful chest-thumping intended to demonstrate that he is the toughest one on the international block, and on the other, his deep conviction that American involvement in the Middle East since the attacks of Sept. 11, 2001, has been a waste of blood and treasure.