Donald Trump can end the war between Russia and Ukraine — but he needs to know where he stands with Vladimir Putin, Ukraine’s President Volodymyr Zelenskyy said.

“Russia is simply lying to Trump,” Zelenskyy said in a Wednesday interview with the Axel Springer Global Reporters network, of which POLITICO is a member. “Most heads of state and government share my opinion, and I very much hope that America sees and understands this. That is the most important thing. How you respond to that is America’s decision.”

The leverage to end the war lies with Trump, Zelenskyy said, because “Putin understands nothing but strength, and America has that strength.”

Referring to Trump, Zelenskyy said: “It’s all in his hands … How strong the sanctions package will be, depends on him. The speed with which decisions are made depends on him.”

Since Trump returned to the White House, he has shown little interest in pressuring Putin, but instead has squabbled with Zelenskyy, culminating in the infamous Oval Office blow-up in late February.

Asked about the incident, Zelenskyy said wryly: “I don’t think it brought us any closer.” He added: “But that was in the past. And today we must do everything we can to ensure that the next meeting in the Oval Office is successful for both countries.”

The U.S. and Ukraine have resumed “constructive” dialogue, including a one-on-one conversation between the presidents at the Vatican in April, which was “friendly,” Zelenskyy said.

With peace negotiations in Istanbul yielding few results and Russia continuing its barrage of Ukraine, Trump signaled frustration with Putin and expressed doubts about Moscow’s willingness to make peace. But after talking with Putin on the phone last week, Trump compared Ukraine and Russia to two squabbling children and claimed the deadline for imposing more sanctions on Moscow is “in his brain.”

Asked if he thinks Trump changes his mind every day depending on whom he has spoken with on the phone, Zelenskyy replied: “I don’t know.”

But he added: “Trump sees that the Russian side is not entirely honest about the war. Russia is not sincere.”

Though he acknowledged recent Russian advances on the frontlines, Zelenskyy insisted Moscow has not achieved its aims in the war and is slowly bleeding out. Putin knows the Russian economy is suffering and is trying to buy time, Zelenskyy said. Stronger sanctions would further deplete Russia’s arsenal, he said, leading to fewer attacks on Ukraine.

Russia can only win if Western partners abandon Ukraine, Zelenskyy said — an American withdrawal would be a “perfect scenario” for Putin.

At the end of the interview, when asked how often he has doubts, Zelenskyy noted that even Winston Churchill felt moments of despair when fighting Nazis in World War II.

“I have no fewer doubts than anyone else in Ukraine. But the difference is that I am the president,” he said. “So until the end of the war, I will never show any moments of weakness. And I will never share my dark days with anyone.”