Donald Trump’s return to the White House could mark a turning point for Ukraine in the war against Russia’s invasion, and potentially an end to U.S. support for Kyiv’s war effort.

Trump and his running mate, vice-president-elect JD Vance, have openly railed against continuing American military and financial aid for Ukraine and have vowed to push a negotiated end to the war — one that could include giving up Ukrainian territory seized by Russia in its nearly three-year-long assault on the country.

Ukrainian President Volodymyr Zelenskyy, who has repeatedly stressed that Russia must be forced into a peace deal on Ukraine’s terms, congratulated Trump on his victory Wednesday morning and expressed confidence in working together to bring the war to an end.

“I appreciate President Trump’s commitment to the ‘peace through strength’ approach in global affairs,” Zelenskyy wrote on social media. “This is exactly the principle that can practically bring just peace in Ukraine closer. I am hopeful that we will put it into action together.”

Zelenskyy had posted that he spoke with Trump to congratulate him.

“We agreed to maintain close dialogue and advance our cooperation. Strong and unwavering U.S. leadership is vital for the world and for a just peace,” he wrote.

But Zelenskyy may face a frosty reception from Republicans in Washington, who are on track to control both chambers of Congress, after the Ukrainian president publicly criticized Trump and Vance and appeared with Democrats during his most recent U.S. trip during the election campaign, angering GOP lawmakers.

“There is a lot of uncertainty that is going to cloud a lot of what happens,” said Oleksa Drachewych, a professor at Western University who specializes in Ukrainian and Russian history and politics.

“The worst-case scenario is that the U.S. support for Ukraine just stops.”

The uncertainty comes as Ukraine faces yet another winter of punishing Russian missile barrages on critical infrastructure, as well as the arrival of thousands of troops from North Korea. The war has been in an effective stalemate for over a year, and both sides have continued to mount casualties.

Trump met with Zelenskyy in New York in September, where the Ukrainian leader detailed his “victory plan” that includes Ukrainian membership in NATO, the return of all territory taken by Russia during the war, and Russian funds for Ukraine’s reconstruction. The plan proposes that Ukrainian forces would become a new European defensive line against Russia and that Ukraine would develop a domestic military industrial base that would gradually replace its reliance on western weaponry.

Following the meeting, Trump and Zelenskyy both expressed confidence in their relationship and a commitment to seeing an end to the war, but Trump also noted his “good relationship” with Russian President Vladimir Putin.