PRESIDENT TRUMP’S decision to strike a Syrian air base in response to a chemical weapons attack by the regime of Bashar al- Assad was right as a matter of morality, but it could also yield a host of practical benefits. The Assad regime may be deterred from again using deadly gas on civilians — a heinous war crime that, if tolerated, would make not just Syria but the world more savage.

Russia and Iran should have new cause to consider whether they will continue backing the blood-drenched Damascus dictator, or cut a deal to get rid of him. Other rogue regimes and their sponsors will have to recalculate how the United States might respond to their provocations. How convenient that Chinese President Xi Jinping, who props up North Korean dictator Kim Jong Un while conducting a slow campaign of aggression in the South China Sea, had a ringside seat in Mar-a-Lago as Mr. Trump boldly acted.

Perhaps most importantly, U.S. allies now have reason to hope that Mr. Trump could fill the leadership vacuum, in the Middle East and beyond, left by President Barack Obama’s decision not to enforce his own red line on Syria’s use of chemical weapons. It is little wonder that Mr. Trump’s action was cheered from Britain to Germany and from Israel to Japan — and by congressional Democrats as well as Republicans. Even the snarling response from Vladi­mir Putin’s Kremlin looked skin-deep, particularly as the Pentagon took care to warn Russia’s forces in Syria in advance.

What’s unknowable is whether Mr. Trump’s decision represents a change in his conception of U.S. foreign interests or a one-off response to wrenching televised pictures of suffocating children. In 2013, Mr. Trump strenuously opposed U.S. retaliatory action following a much more deadly sarin gas attack by the Assad regime; just Tuesday, he repeated in a speech that “I’m not, and I don’t want to be, the president of the world.” Yet on Thursday night Secretary of State Rex Tillerson spoke of taking action “on behalf of the international community” to preserve “international norms” about chemical weapons, and Mr. Trump said that “as long as America stands for justice, then peace and harmony will, in the end, prevail.” America’s allies can only hope that Mr. Trump will truly embrace that sentiment, rather than his long-standing isolationist instincts, as his presidency evolves.

For now, Mr. Trump must devise a Syria policy that responds to this week’s events. The administration now appears to understand that the civil war — and the fuel it provides for the Islamic State and other extremists — can never be ended while the Assad regime remains in power. The chemical attack signaled the regime’s intention to assault rebel-held Idlib province with the same scorched-earth tactics it has employed elsewhere in the country, which would trigger a massive new wave of refugees in addition to thousands more civilian deaths. The United States should make clear to Damascus that any further chemical attacks — as well as other blatant assaults on civilians — will be met with more military retaliation.

(The Washington Post)

The administration should, meanwhile, make another effort to draw Russia and Syria’s neighbors into a negotiation on the country’s future, using the new leverage provided by Mr. Trump’s demonstrated willingness to use force. It should seek bipartisan congressional support, including the authorization of military force in the event of further atrocities — even if the White House has, as we believe, the constitutional leeway to act without it.

Mr. Trump has created an opportunity for the United States, and for his presidency, in Syria. Its ultimate value will depend on how well he follows up.