Two years ago, Gen. Mark A. Milley, then the chief military adviser to President Biden, suggested that neither Russia nor Ukraine could win the war. A negotiated settlement, he argued, was the only route to peace.

His remarks caused a furor among senior officials. But President-elect Donald J. Trump’s win is turning General Milley’s prediction into reality. Mr. Trump has made clear his distaste for continuing to help Ukraine take back territory seized by Russia, making a negotiated settlement the only real viable option left.

The ascendance of Mr. Trump as Ukraine suffers losses on the battlefield in fact means less room for Ukraine to maneuver.

One of the biggest unknowns for Ukraine is whether the Trump administration and Europe will provide any kind of security guarantees that would prevent Russia from trying to take more territory. Mr. Trump has said he would end the war quickly, though he has not explained how. But Vice President-elect JD Vance has outlined a plan that would allow Russia to keep the Ukrainian territory it has taken.

A phone call just after the election between Mr. Trump and President Volodymyr Zelensky of Ukraine shed little light on the question of security guarantees. Aides to both men simply described the tone of the call as “positive.”