White House Worries Russia’s Momentum Is Changing Trajectory of Ukraine War

Just 18 months ago, White House and Pentagon officials debated whether Russia’s forces in Ukraine might collapse and be pushed out of the country entirely.

Now, after months of slow Russian ground advances and technological leaps in countering American-provided arms, the Biden administration is increasingly concerned that President Vladimir V. Putin is gathering enough momentum to change the trajectory of the war, and perhaps reverse his once-bleak prospects.

In recent days, Moscow’s troops have opened a new push near the country’s second-biggest city, Kharkiv, forcing Ukraine to divert its already thinned-out troops to defend an area that it took back from Russian forces in a stunning victory in the fall of 2022.

Artillery and drones provided by the United States and NATO have been taken out by Russian electronic warfare techniques, which came to the battlefield late but have proven surprisingly effective. And a monthslong debate in Washington about whether to send Ukraine a $61 billion package of arms and ammunition created an opening that Russia has clearly exploited, even though Congress ultimately passed the legislation.

In interviews, American officials express confidence that many of these Russian gains are reversible once the spigot of new arms is fully opened, most likely sometime in July, and President Volodymyr Zelensky of Ukraine finds ways to bring more — and younger — troops to the front lines. But they are hesitant to offer predictions of where the battle lines may stand even a few months from now, or whether Mr. Zelensky will be able to mount his long-delayed counteroffensive next year, after one last spring fizzled.

American and allied officials interviewed for this article spoke on the condition of anonymity, in order to discuss intelligence reports and sensitive battlefield assessments. But some of the concerns have spilled out in public comments.