For all the disarray and unfairness of President Trump’s approach to the war in Ukraine, he is right about a few big things. He is right that the war’s continuing human carnage is a tragedy, given the unlikelihood of a military breakthrough for either side after more than three years of fighting. He is right that ending the war could open the way to economic development in both Ukraine and Russia and help the global economy, too. And he is right to be frustrated with President Vladimir Putin’s intransigence and recent acceleration of bombing in Ukraine.

But Mr. Trump would be profoundly wrong to walk away from cease-fire talks, as he keeps threatening to do.

An American withdrawal would only encourage a new military push by Mr. Putin, who has staked his authoritarian rule on bringing Ukraine to heel and seizing its territory. Nor would Ukraine surrender. It has developed ways to hold back Russian forces, including through a domestic defense industry that may produce a few million drones this year. Other European powers, including Britain, Germany and France, will also continue to support Ukraine.

Rather than walk away, Mr. Trump has an opportunity to increase the pressure on Russia and Ukraine to agree to a deal. In the past few days, he has even shown signs of doing so (hard as it is to know when his words reflect his intentions). He said on Wednesday that he was “not happy” with Mr. Putin’s recent attacks on Ukraine and said on Monday that he was “absolutely” considering new economic sanctions on Russia.

Both sides have reasons to consider a truce. Ukraine has continued to lose territory, while Russia’s progress has been extremely costly in terms of casualties and destroyed equipment. Over the past year, Russia has gained only about 0.6 percent of Ukraine’s territory, and hundreds of thousands of its soldiers have been wounded or killed, The Washington Post reported. That is not a sustainable ratio.

The outlines of a likely deal are clear enough. Russia would keep territory that it controls in Ukraine’s east and south, including the Crimean Peninsula. It would also receive promises from the West to lift economic sanctions and not to admit Ukraine to NATO. For Ukraine, the West could commit to military and economic support if Russia attacks again and, more immediately, to integrate Ukraine even more closely into the European economy. Ukraine’s resilient, talented population would then have an opportunity to thrive.