Message sent. President Trump made it clear with a strategic cruise missile attack on a Syrian air base that his administration will act unilaterally to enforce international prohibitions against the use of chemical weapons. The missile strikes came Thursday night in response to a sarin gas attack carried out by Syrian forces on civilians in a rebel-held community.

Trump sanctioned an attack that was limited in nature to minimize the chances that it would result in conflict escalation. The administration reportedly gave advance information of the strike to Moscow, reducing the chances that the attack would lead to a confrontation between Russian and U.S. forces.

While it appears the attack did not significantly degrade the ability of President Bashar Assad’s military to continue his war against rebel factions, with its focus on civilians, Assad and his Russian enablers at least know that the U.S. won’t tolerate the use of chemical weapons.

It’s an arbitrary line. Assad has also violated international norms in targeting schools and hospitals, employing barrel and cluster bombs in the process. But it’s a line.

There is also the inescapable irony that the president, who said he was moved by the photos of children killed in the chemical attack, continues to pursue a policy that seeks to block humanitarian groups in this nation from assisting refugees who are victims of Assad’s repugnant campaign. Perhaps he will reevaluate that stance.

Was there a political calculation? Almost certainly. The president has been off to a tough start on domestic policy, seeing his travel bans twice rejected by the courts and the effort to repeal and replace the Affordable Care Act fail. And there is that little matter of Russian meddling in the 2016 presidential election and possible collusion in those efforts by some associated with the Trump campaign.

An attack on a certified bad guy such as Assad, delivering a black eye to Assad’s ally Russia in the process, is a sure way to boost approval ratings and change the national discussion, at least in the short term.

What this means for Trump’s overall strategic outlook is unclear. Up to this point the president has signaled an isolationist approach, noting he is not the “president of the world.” The challenge ahead is reconciling that position with this attack and clarifying what other lines will invite future military responses.