Moscow kills a chemical weapons investigation to help Syria’s Assad.

Russia refused last week to renew the mandate of a United Nations panel investigating Syria’s chemical weapons use, and the veto is more than Vladimir Putin’s usual intransigence. The Russian rejection is a public embarrassment for the Trump Administration, which earlier this month claimed Moscow is helping to advance U.S. goals in Syria.

The Joint Investigative Mechanism, or JIM, was the rare U.N. creation, like the U.N. commission on North Korean human-rights abuses, that did meaningful work. Since its creation in August 2015, the panel found Bashar Assad’s regime responsible for three chlorine and sarin gas attacks and also exposed Islamic State’s use of mustard gas.

The JIM’s mandate was set to expire Thursday evening, and Russia’s Security Council veto sealed its fate. Moscow argued that the JIM was a spectacle meant to undermine Mr. Assad, which is of a piece with Russia’s larger propaganda campaign to paint the presence of U.S. Special Forces and the U.S.-backed Syrian Democratic Forces in Syria as an illegal occupation.

U.S. Ambassador to the U.N. Nikki Haley responded via Twitter that, “By using the veto to kill a mechanism in Syria that holds users of chemical weapons accountable, Russia proves they cannot be trusted or credible as we work towards a political solution in Syria.”

That’s exactly right, but someone should tell President Trump and Secretary of State Rex Tillerson. Earlier this month the State Department announced a deal with Russia to expand “deconfliction zones” in southwestern Syria and eventually to eject Iran-backed fighters from the country.

An Administration official said on background during Mr. Trump’s Asia trip that the deal proved that “despite our many differences with Russia, our two countries are capable of working together on difficult problems where interests converge and our doing so is profoundly in our national security interest.” A statement from Foggy Bottom said President Trump thinks the deal “will save thousands of lives.”

Russia has since used its air power to protect Iran-backed ground forces as they march toward the Syrian Democratic Forces, and it is disputing that foreign fighters should head home. Now comes the veto of the chemical weapons investigators. If this shows interests converging, how would the White House define differences?

Meanwhile, moderate Sunni Arabs who once might have been U.S. allies are increasingly turning toward local al Qaeda affiliates, and Iran and Syrian forces backed by Russia are dominating larger swaths of territory at the expense of Kurds and Arabs who fought hard to defeat Islamic State. As the JIM’s demise shows, none of this will change until the Trump Administration is willing to do more than cede Syria to the Syria-Iran-Russia axis.

Appeared in the November 20, 2017, print edition.