RUTHFULLY YOURS

The 105 Tomahawk and standoff air missiles, launched from three directions into Syria, did tangible damage to Syria’s chemical-weapons R&D and storage facilities. Lt. Gen. Kenneth McKenzie told reporters, “no Syrian weapon had any effect on anything we did,” including Russian-supplied missile defenses.

The damage might have a deterrent effect on Assad’s use of chemicals, given that Mr. Trump said Friday he is prepared to enforce the ban again. Mr. Trump lost credibility on that score in the last year after his Administration concluded several times that Assad had used chlorine gas but took no action. Next time the attack should be even more punishing.

The military contribution from Britain and France was useful in demonstrating a larger willingness to prevent the normalization of WMD. And the strike could have a demonstration effect on North Korea as Mr. Trump heads into his perilous summit with Kim Jong Un.

***

Yet one bombing won’t change the fundamentals of the Syrian battlefield, or the strategic reality that the Russia-Iran-Assad axis is winning. By Sunday Assad had already resumed bombing rebel areas, including civilian homes. To alter those realities, Mr. Trump has to do more than plead with the Russians and Iranians as he did Friday night:

“To Iran, and to Russia, I ask: What kind of a nation wants to be associated with the mass murder of innocent men, women, and children?” The answer is they do.

And the only way to change their minds is to change their recognition of the costs and benefits of intervention.

One useful step would be keep the pressure on Russia to fulfill its agreement to eliminate chemical arms from Syria. Russia surely knew about the stockpiles, and the U.S. should demand that the United Nations office in Damascus inspect the chemical attack areas. It should also insist on U.N. access to all areas needing humanitarian aid. If Syria refuses, the U.N. should cease all such aid to the country since most of it now goes to the regime.

More broadly, Mr. Trump needs a strategy for putting pressure on the Syrian axis and gaining leverage in talks to end the civil war. The best idea we’ve seen would follow the example of President George H.W. Bush after the first Gulf War in 1991.

The U.S. and its allies established and enforced a no-fly safe zone in northern Iraq that protected the Kurdish areas from attacks by Saddam Hussein. The plan worked for a decade and allowed the Kurds to build the most prosperous, pro-American part of Iraq.

The U.S. already operates a de facto safe zone east of the Euphrates River with some 2,000 troops. But a zone there and another near the border with Jordan might require fewer troops once Islamic State fighters are further reduced. Such a zone would allow refugees to return safely, easing pressure on nearby states. It would give the U.S. leverage over Kurds and Arabs under protection to help against a revival by Islamic State or al Qaeda. And that might help ease tensions with the Turks.

Such a zone wouldn’t threaten Assad’s control over the rest of Syria, but the U.S. has called for Assad’s ouster for seven years without effect. Better to accomplish what we can than to keep tilting at what we can’t.

Above all, the safe-zone strategy would send a signal that the U.S. isn’t abandoning the region to Iran and Russia. Iran’s strategy is to use southern Syria as a second base, along with Lebanon, for Hezbollah militia and arms on the border with Israel. This would make an Israeli-Iran conflict inevitable, and the U.S. would be drawn in eventually.

The better U.S. strategy is to support regional opponents of Iranian imperialism and try to turn Syria into the Ayatollah’s Vietnam. Only when Russia and Iran begin to pay a larger price in Syria will they have any incentive to negotiate an end to the war or even contemplate a peace based on dividing the country into ethnic-based enclaves.

***

Executing such a strategy would require considerable diplomacy, as well as persuasion and commitment by Mr. Trump at home and abroad. Perhaps that is beyond his interest or capacity. But this Administration still has three years to run, and what former General David Petraeus once called the “geopolitical Chernobyl” of Syria is far from contained.

Barack Obama dealt Mr. Trump a bad hand by letting Russia, Iran and China believe they could advance their goals of regional domination without U.S. resistance. In Syria as elsewhere, Mr. Trump has to decide if he wants to ratify that American retreat or develop a strategy to stop it.