Children peer out from a damaged home in Aleppo, Syria, on Feb. 11. (Alexander Kots/Associated Press)

WITHIN HOURS of voting for a U.N. Security Council resolution in December mandating an end to the bombing of civilians and the delivery of humanitarian aid in Syria, Russia dispatched planes to pound a town held by U.S.-backed rebels. As Syrians in besieged towns continued to starve, Moscow joined with Iran in supporting a broad offensive that has allowed the regime of Bashar al-Assad to retake control of key areas around the city of Aleppo, while cutting off the supply lines of 400,000 more civilians.

The Obama administration responded to this ruthless and criminal strategy by soliciting Moscow’s terms for a truce. Early on Friday in Munich, it weakly agreed to a bad deal that will allow the Russian-Iranian-Assad forces to consolidate and expand on their gains, and to occupy a commanding position in any negotiation about Syria’s future. Hours later, Russian planes were bombing again.

The salient feature of the agreement struck by Secretary of State John F. Kerry is a partial cessation of hostilities — a week from now. That will allow Russian planes to continue an aerial campaign that, as documented by human rights groups, has included dropping cluster munitions on civilian areas. It could allow Shiite fighters from Lebanon and elsewhere, commanded by Iran, to cut off the last supply route to the half of Aleppo held by U.S.-supplied rebel forces. That would put Moscow and its allies closer to their principal goal — which is to eliminate any forces in Syria other than the Assad regime and the Islamic State. If they don’t succeed in a week, Russia has given itself leave to continue bombing “terrorist” groups, which it defines as including the rebels in Aleppo.

For the West, the reward of accepting all this is the promised opening of humanitarian access to civilian areas subjected to a “surrender or starve” siege strategy, such as the town of Madaya, where some 20,000 civilians are trying to survive by eating grass and insects, and children are dying of starvation. U.N. officials say they hope blockades will be lifted and aid delivered by early next week; but this is not the first or second time such promises have been made. As Mr. Kerry put it, “what we have here are words on paper. What we need to see in the next few days are actions on the ground.”

Vladi­mir Putin’s record does not suggest such actions will be extend beyond the token. In Syria, the Russian ruler has pursued the same tactics he adopted in Ukraine: gain a decisive military advantage, then offer lopsided terms for a cease-fire. After winning far-reaching political concessions in Ukraine, Mr. Putin never respected the cease-fire or subsequent security measures his envoys agreed to; fighting continues to this day. In Syria, he has less reason to keep his word, as no Western sanctions, nor any other tangible measures, penalize his intervention there.

Mr. Kerry continues to suppose that sheer jawboning will eventually persuade Mr. Putin to abandon the Assad regime and agree to a political settlement that ousts the Assad clique and empowers Syria’s Sunni majority. In the real world, the best-case scenario after five years of U.S. inaction is a partial peace that leaves Syria partitioned into zones controlled by the regime and the Islamic State, with a few opposition and Kurdish enclaves squeezed in. Even that would require the Obama administration to aggressively step up its military support for rebel groups, and confront Russia with more than rhetoric. There was no hint of such U.S. resolve in Munich.