AFTER AN agreement to “de-escalate tensions and restore security” in Ukraine was announced Thursday, Secretary of State John F. Kerry was very explicit about U.S. expectations. “We fully expect the Russians . . . to demonstrate their seriousness by insisting that the pro-Russian separatists who they’ve been supporting lay down their arms [and] leave the buildings” in eastern Ukraine, he said. “I made clear to Foreign Minister [Sergei] Lavrov today that if we are not able to see progress . . . this weekend, then we will have no choice but to impose further costs on Russia.”

The weekend has come and gone, and far from standing down in eastern Ukraine, Russia has continued to escalate. Its operatives and those they control have not withdrawn from the government buildings they occupy. In Slovyansk, the crossroads where Russian military operatives appear to be headquartered, a shooting incident early Sunday morning has been seized on by Moscow’s crude propaganda apparatus, which is claiming — based on what looks like fabricated evidence — that a Kiev-based right-wing group was involved.

On Monday, Mr. Lavrov was back to threatening an invasion by the tens of thousands of Russian troops on Ukraine’s border, claiming that, in the words of his ministry, “Russia is increasingly called upon to save southeastern Ukraine from chaos.”

Again Vladi­mir Putin is flagrantly disregarding the warnings and “red lines” of the Obama administration. He has reason to do so: President Obama also doesn’t observe them. Despite Mr. Kerry’s clear words, sanctions that have been prepared against cronies of Mr. Putin and companies involved in his Ukraine ad­ven­ture remain on ice at the White House, where they have languished for more than a week. When asked Monday how much longer they would be held back, White House spokesman Jay Carney said, “I don’t have an end date for you.”

Vice President Biden arrived in Kiev on Monday and is expected to announce more U.S. aid. But steps such as providing nonlethal equipment to the dysfunctional Ukrainian army will not stop a Russian invasion or induce Mr. Putin to comply with last week’s Geneva agreement. Perhaps nothing will; but the only strategy with a chance of working is to follow through on the administration’s own rhetoric. When the Russian-backed operatives first began taking over buildings in Donetsk and other cities two weeks ago, Mr. Kerry told a congressional hearing that broad sanctions against the Russian banking, energy and mining sectors were “on the table.”

Those steps would give pause to the Russian elite, if not Mr. Putin. Fear of them probably induced Mr. Lavrov to sign on to the de-escalation plan, as a way of preventing the West from acting. Yet now White House aides are waving off the “sectoral” sanctions Mr. Kerry spoke of and are delaying even more modest steps against individuals. They claim that the United States shouldn’t act independently of the European Union — which gives Greece and Cyprus a veto over how the Obama administration reacts to the crossing of its own publicly declared red lines.

For weeks Mr. Obama has held back on forceful measures against Mr. Putin’s aggression in Ukraine on the theory that a measured approach matched with diplomacy would yield results. The policy has failed. Now Mr. Obama must act — or doom Ukraine to dismemberment.