NEARLY TWO weeks after the U.N. Security Council passed a resolution mandating a 30-day cease-fire in Syria, Russian and government forces are unrelentingly pursuing one of the bloodiest and most brutal offensives of the war. They are attempting to overrun the rebel-held area of Eastern Ghouta, outside Damascus, where nearly 400,000 people have been besieged since 2013. Scores of people are being killed each day; the Syrian Observatory for Human Rights counted 93 on Wednesday alone. There have been numerous reports of attacks on hospitals and schools and of the use of chlorine gas — all of which are war crimes.

Tragically, there is little new in this, apart from the intensity. Over and over, the government of Bashar al-Assad and Russia have accepted cease-fires, or “humanitarian pauses,” or “de-escalation zones” in Eastern Ghouta, only to continue their attacks. Their brazenness is enabled by the unwillingness of any other power to enforce U.N. resolutions, or the Chemical Weapons Convention, or to otherwise punish the regime or Russia for their crimes.

There is, at least, reason to hope that the impunity will not last forever. Since 2011, a U.N. commission has been meticulously gathering evidence of war crimes in Syria for presentation at the U.N. Human Rights Council, and eventually to international and national courts. Its latest report, covering the period from last July until January, offers horrifying detail about the Russian-Syrian depredations in Eastern Ghouta.

The siege, the report says, has been “characterized by pervasive war crimes, including the use of prohibited weapons, attacks against civilian and protected objects, starvation leading to acute malnutrition, and the routine denial of medical evacuations.” Hospitals and schools have been systematically bombed; on a single day, Nov. 8, three schools were struck from the air. Hundreds of medical workers have been killed or injured in airstrikes, and women have begun giving birth at home rather than risk going to a hospital.

The United Nations documented three uses of chlorine against rebel fighters in July, and another attack in November in which a phosphorus-based pesticide was used. These are carefully calibrated atrocities. President Trump ordered a retaliatory strike following the regime’s use of nerve gas last year, but he has not responded to chlorine attacks. And so they continue.

Russian forces also target civilians, and the United Nations documented one incident it says “may amount to a war crime.” Last Nov. 13, a Russian plane was observed carrying out a series of airstrikes on the main market as well as surrounding houses in the town of Atarib, in Aleppo province. The report says at least 84 people were killed, including six women and five children. It said the plane dropped unguided “blast weapons,” even though “the use of such weapons in a densely populated area was certain to impact civilians.” That, no doubt, was the intention.

As the Ghouta offensive has continued, the State Department has objected; spokeswoman Heather Nauert castigated Russia on Twitter. The trouble is, Moscow knows that Mr. Trump feels differently. When he was asked about Eastern Ghouta, on Feb. 23, the president reiterated his view that the only U.S. interest in Syria was “to get rid of ISIS and to go home.” For the Assad regime and Russia, that’s an open invitation to continue gassing children, bombing hospitals and committing other war crimes.