European nations are increasingly optimistic that they can support Ukraine financially and militarily against Russia even if President Trump decides to wash his hands of the conflict, as he often threatens, and instead focuses on normalizing relations with Moscow.

But even with their best efforts, the Europeans cannot replace all of what the United States provides Ukraine — most important, real-time intelligence about Russian forces, incoming missiles and how and where to target the enemy. Ukraine’s ability to fight effectively relies largely on that American intelligence.

“The Ukrainians don’t want this to be cut off no matter what,” said Camille Grand, a former NATO assistant secretary general. American intelligence is so sophisticated that it tells the Ukrainian military where Russian brigade headquarters are, where to target missiles and where to aim air defenses against incoming missiles, he said.

Despite Mr. Trump’s complaints about Ukraine, the United States has continued to provide intelligence to Kyiv, save for a pause for a few days after Mr. Trump took umbrage with President Volodymyr Zelensky in the Oval Office. It has also delivered weapons and equipment authorized by Congress during former President Joseph R. Biden Jr.’s administration. But that authorization, about $61 billion, is expected to run out in the next few months, and there is no talk in Washington of another appropriation of funds.

NATO defense ministers are expected to focus on spending goals and aid to Ukraine at meetings on Wednesday and Thursday in Brussels. Though Ukraine launched one of its most ambitious attacks yet in Russia over the weekend and attacked a key bridge on Tuesday, the issue is increasingly urgent as Ukrainian officials sound alarms about weapons shortfalls and Russia ramps up another offensive.