UKRAINE’S NEW leader is making progress in regaining control over eastern areas of the country that were seized by Russian-backed insurgents, but he’s getting no help from the United States or the European Union. In fact, President Petro Poro­shenko is succeeding in large part because he is resisting pressure to make unacceptable concessions to Moscow and its surrogates.

Germany and France have been pressing for a cease-fire and peace talks that would include the rebels, Russia and Ukraine but not Western governments. Vladi­mir Putin is supportive, as he hopes to create another of the “frozen conflicts” Moscow uses to permanently destabilize its neighbors. His truce terms would leave in place Russian control of the major eastern cities of Donetsk and Luhansk and make it virtually impossible for Mr. Poroshenko to stabilize the country.

Mr. Poroshenko’s resistance to those terms and resumption of military action has led to the recapture of half the territory once occupied by the pro-Russian forces, including the important crossroads town of Slovyansk. Ukrainian forces are now encircling the rebels in Donetsk. The Ukrainian leader has offered to talk to the insurgents but rightly says a cease-fire depends on an end to Russia’s arms trafficking.

It remains to be seen whether Ukrainian forces can finish off the insurgents while observing a pledge to avoid civilian casualties and whether Mr. Putin will step up his military support for his proxies. The Russian leader has been playing what NATO’s secretary general correctly termed a “double game,” offering fake compromises to the West while continuing his campaign to make Ukraine ungovernable. Mr. Putin has economic as well as military cards to play: He has suspended Russian gas deliveries to Ukraine and threatened to impose crippling trade tariffs. He has patience and plenty of time; for the moment he is popular at home, and the Russian stock market is rising.

If he has been surprised by Mr. Poroshenko’s grit, then Mr. Putin can only be encouraged by the fecklessness of the European Union and the United States. At the end of June, the allies promised tough sanctions against Russia if Moscow did not immediately stop its support of the rebels. Secretary of State John F. Kerry breathlessly declared on June 26 that Russia had to move within “hours” to disarm its proxies. Two weeks later, the promised “sectoral” sanctions on Russian industries have not been adopted, even though Western governments agree that Mr. Putin has not met any of their conditions. Instead, German Chancellor Angela Merkel and French President François Hollande are leaning on Mr. Poroshenko to stop trying to regain control over his country.

Ukrainian sappers ride on a truck used for neutralizing shells, which were left by pro-Russian fighters in the near of Slaviansk, Ukraine. (Sergey Polezhaka/EPA)

To their credit, senators from both parties voiced frustration with the Obama administration’s continued passivity at a Foreign Relations Committee hearing Wednesday. “What are we waiting for?” asked Chairman Robert Menendez (D-N.J.). Administration officials predicted that the oft-promised sanctions would come “very soon” if Russia did not change course — perhaps following a European Union summit meeting next week. But the White House has not committed itself to unilateral action if the European Union falters.

The administration is not wrong to prefer joint action with the Europeans if it is achievable. But the United States has the power to impose crippling unilateral sanctions on Russia, especially through the banking system. If the Ukrainian government can act without the permission of France and Germany, so can the United States.