AS THE TERRORIST group known as ISIS (Islamic State of Iraq and Syria) rampages across Iraq, the illogic of President Obama’s reluctance to help the moderate opposition in neighboring Syria becomes ever clearer. The Syrian Free Army wants to fight the jihadists. But as ISIS consolidated gains in Iraq last week, the moderates were being pounded by Syrian dictator Bashar al-Assad — and lacked the weapons to fight back. Meanwhile ISIS already is bringing back to Syria sophisticated weaponry it has captured in Iraq.

Mr. Obama has had two primary answers when challenged on his inaction. One, which he repeated last week, is that the moderate rebels just weren’t up to the job — “former farmers or teachers or pharmacists who now are taking up opposition against a battle-hardened regime.” The other is that his diplomacy at least has succeeded in depriving Mr. Assad of his chemical weapons. Now, as Mr. Assad again uses such weapons and stalls on his promise to give up his arsenal, that accomplishment is in doubt.

We welcomed the agreement that the United States and Russia reached last year to compel Syria to rid itself of chemical weapons after a horrific attack that killed more than 1,400 people in August. The plan was ambitious: It called for complete, verified liquidation of Syria’s chemical weapons stocks and production facilities no later than June 30. And the effort to move these hazardous weapons out of Syria has come a long way; an estimated 92 percent of them have been taken out.

But after the initial progress, Assad’s regime has turned truculent and unresponsive. Robert Mikulak, the U.S. representative to the Organisation for the Prohibition of Chemical Weapons (OPCW), last week declared that Syria has missed “a parade of timelines.” He pointed out that Syria’s production facilities were supposed to be destroyed by March, but destruction hasn’t started. None of the remaining 8 percent has moved toward the port of Latakia. Questions remain about Syria’s declaration of its stockpiles.

This is not happening because of housekeeping problems or technical glitches. According to Mr. Mikulak, “Syria has squandered many months now that could have been used to fulfill its obligations.”

On top of this, Syria has now resorted to using chlorine, an industrial chemical, as a weapon. The OPCW sent a fact-finding mission seeking more evidence of chlorine use; that group had to turn back because of fighting. But the team declared that the reports of chlorine use “cannot be dismissed as unconnected, random, or of a nature attributable to purely political motives.” The report added that “toxic chemicals, most likely pulmonary irritating agents such as chlorine, have been used in a systematic manner in a number of attacks.”

Mr. Mikulak pinpointed responsibility: “The systematic nature of the attacks, the intended targets and other publicly available information all point to one likely perpetrator — the Syrian government.”

Mr. Assad’s regime is making a mockery of a once-promising and ambitious effort at chemical weapons disarmament. That is one more reason for the administration to ramp up its support for Syria’s moderate rebels.