IT WAS far from clear Thursday if a new accord on Ukraine would last long enough for the implementation of its first and most tangible provision, a cease-fire set to begin Sunday. If it does, Ukrainians may be spared, at least temporarily, the deaths of more soldiers and civilians and the loss of more territory to Russian aggression. However, the deal brokered by German and French leaders with Russia’s Vladi­mir Putin does little to restrain his ambition to create a puppet state in eastern Ukraine that could be used to sabotage the rest of the country. In fact, in the unlikely event that its terms are fully carried out, the pact would enable his project.

The result of the all-night negotiations in Minsk , Belarus, among Mr. Putin, German Chancellor Angela Merkel, French President François Hollande and Ukrainian President Petro Poroshenko reflected the imbalance between a Kremlin ruler in the midst of using military force and European leaders who not only are unready to respond but who are also trying to prevent Ukraine from obtaining the means to defend itself. In exchange for the promise of a “deescalation” that was their overriding goal, the European leaders induced Mr. Poroshenko to accept terms that give Mr. Putin a veto over any final political settlement in eastern Ukraine — and permission to continue violating the country’s sovereignty in the meantime.

Most significantly, control over the border between Russia and Ukraine would not be returned to Kiev until the end of the year — and then only after a “constitutional reform” acceptable to Moscow and its surrogates grants powers to Russian-controlled regions. Without border control, Ukraine cannot prevent Russian forces, supplies and agents from flowing across. While the deal promises a withdrawal of “foreign armed formations” from Ukraine, there is no deadline — and Mr. Putin’s contention is that NATO has “legions” in the country but Russia does not.

No wonder that Mr. Poroshenko emerged from the talks saying that “the main thing that has been achieved” is the promised Sunday cease-fire, along with a pullback of heavy weapons by both sides over the following two weeks. Even that prospective respite was clouded by Mr. Putin’s assertion that thousands of Ukrainian troops defending the strategic crossroads of Debaltseve must “lay down their arms.” That would reward the latest Russian offensive by transferring de facto control over the town to the separatist statelet Moscow is constructing.

Nor is that Mr. Putin’s only gain. By going along with the Europeans’ desperate diplomatic gambit, he ensured that not even minor sanctions would be adopted at a European Union summit Thursday. He also provided President Obama with reason to overrule those in his administration seeking to supply arms to Ukraine. Mr. Putin can resume military aggression at will, while the push for new sanctions or weapons could take weeks or months to regain momentum.

Mr. Obama was content to stand back while Germany and France struck the deal, and the State Department quickly endorsed it. The administration rightly said that it would consider easing existing sanctions on Russia only when the agreement is “fully implemented,” including “the withdrawal of all foreign troops and equipment from Ukraine [and] the full restoration of Ukrainian control of the international border.” But without additional economic and military pressure, Mr. Putin will never meet those terms.