President Donald Trump’s relations with, and intentions toward, the Russian regime of Vladimir Putin remain troublingly opaque. So it was a pleasant surprise on Tuesday when his ambassador to the United Nations, Nikki Haley, excoriated Moscow for blocking action against the Syrian regime of Bashar al-Assad for its illegal use of chemical weapons.

Haley was only stating plain truths. An investigation ordered by the U.N. Security Council concluded months ago that Syrian government forces dropped chlorine-filled barrel bombs on rebel-controlled areas three times in 2014 and 2015 — a blatant violation of the Chemical Weapons Convention that the Assad regime joined in 2013. In reality, Damascus has used the horrific weapons considerably more often than that. Yet Moscow and Beijing refused to accept the evidence and tried to put off a vote on sanctioning those found responsible for the attacks.

Haley, who lunched with Trump and Vice President Mike Pence the day before the Security Council’s meeting, insisted on a vote so that the Putin and Xi Jinping regimes were forced to go on the record. Then she bluntly called them out.

The ambassador’s forceful diplomacy was useful for more than sending the message that the Trump administration will be, like all U.S. administrations before it, ready to oppose war crimes. We hope it also is meant to put Putin on notice that Trump’s stated willingness to join with him in fighting the Islamic State will not extend to tolerating gross human rights violations or propping up the blood-soaked Assad dictatorship. An alliance with Russia that abetted such actions would only discredit the United States, including with its major allies in the Middle East; the chief beneficiary would be Iran, which has made the Assad regime its puppet and which has the largest interest in sustaining it.

Putin, who has frequently hinted that he could be willing to dispense with Assad, has been trying to orchestrate a new Syrian peace process with Turkey that all but excludes the United States. Predictably, it is going nowhere — in part because, as The Washington Post’s Liz Sly reports, players on both sides are waiting to see what stance the new U.S. administration adopts. This is leverage that Trump should use: If Putin wants his help to settle the Syrian conflict and protect Russia’s interests there, he should be obliged to split with Iran and abandon a regime that drops chlorine on women and children.

Editorial by The Washington Post