In the aftermath of President Donald Trump’s public suggestion on Sunday that Syrian President Bashar al-Assad would be made to pay a “big price” for the government’s use of chemical weapons in Syria’s ongoing civil war, the international community has braced for another limited U.S. military strike against Syria. The presumed goal would be to remind Mr. Assad that his actions have consequences and that the United States will not stand idly by while chemical weapons are used in violation of international law and previous agreements with Syria. President Trump has also publicly taunted Russia: “Get ready Russia, because they will be coming!”

But is the best solution to this ongoing problem the use of military force? Can a resort to force at this point be justified, either morally or pragmatically? It should go without saying that Mr. Assad’s actions must have consequences, lest the world’s geopolitical bullies be emboldened further, including Syria’s ally and sponsor, Vladimir Putin. But the unforeseen consequences of military strikes make it clear that the jus ad bellum precepts of just war theory cannot be fulfilled in this circumstance. There is no real probability of success in stopping Mr. Assad or preventing future atrocities through a use of limited force.

If the aims of the United States are humanitarian and sincere, it cannot continue to bar the innocent bystanders of this conflict from the refuge they so desperately seek.

The presumed value of proving to Mr. Assad that his warmaking capacity will be compromised if he flouts international law is severely diminished by the danger of provoking a far more perilous conflict if U.S. weapons accidentally kill Russian or Iranian soldiers. Russia has already publicly vowed to retaliate if its troops are harmed.

One could hardly give Mr. Assad a greater public-relations boon—or a pretense to strike with chemical weapons again while the world teeters on the break of global war. The material effect of a missile strike would also be limited—and Mr. Assad knows the United States has no stomach for another ground war in the Middle East—perhaps even for the kind of sustained aerial campaign that could significantly cripple the war-making capacity of government forces.

For the nation’s credibility and for its moral probity, the Trump administration must stop treating Syrian refugees like terrorist threats rather than war victims deserving of sanctuary.

It is also worth asking whether this represents a moment of last resort with Mr. Assad. Further sanctions—including ones aimed at Russia, whose malign intentions in Syria seem clear—remain an option. So, too, does the possibility of creating an international coalition to pressure Syria militarily, rather than relying on unilateral action and online bluster. Unfortunately, only last week Mr. Trump instructed his military advisers to begin planning for the withdrawal of the 2,000 U.S. soldiers currently in Syria assisting anti-ISIS efforts—the opposite response from this week’s bellicose threats, but equally damaging for the stability of the region.

Crucial, too, is proving the sincerity of U.S. aims on the international stage after previous ill-fortuned interventions in the region in recent decades. By last fall the United States had spent an estimated $2.2 billion supplying weapons to various factions on the ground in Syria, roughly three times the amount of humanitarian aid offered to Syrian victims of violence. Imagine if the U.S. military infusion was matched dollar-for-dollar by humanitarian aid. When our weapons expenditures are three times our spending on basic human needs, we can hardly claim our goal is first and foremost to alleviate the suffering of the people of Syria.

Finally, both for the nation’s credibility and for its moral probity, the Trump administration must stop treating Syrian refugees like terrorist threats rather than war victims deserving of sanctuary in the United States and elsewhere according to the dictates and intentions of international law. If the aims of the United States are humanitarian and sincere, it cannot continue to bar the innocent bystanders of this conflict from the refuge they so desperately seek.