File Photo: Ukrainian President Volodymyr Zelenskyy poses for a photo after his interview with The Associated Press in Kharkiv, Ukraine, AP
Zelenskyy, who was in Argentina over the weekend, was due to deliver a 12:00 pm (1700 GMT) address to the National Defense University in Washington, following an introduction by US Defense Secretary Lloyd Austin, the Pentagon said.
On Tuesday, Zelenskyy was scheduled to meet with President Joe Biden at the White House and also with congressional leaders, including the recently elected Republican leader of the House of Representatives, where the mood on the far-right of the party has turned sharply against Ukraine.
White House press secretary Karine Jean-Pierre said that Zelenskyy's visit would "underscore the United States' unshakeable commitment" to Ukraine, which in February will enter its third year of battling an all-out invasion attempt by Russia.
Throughout the bloody conflict, which has seen swaths of Ukraine destroyed and millions driven from their homes, Ukrainian forces have depended heavily on a US-led coalition of countries delivering tens of billions of dollars in ammunition, weaponry, and economic and social aid.
Now the flow of US aid, described by Biden as part of an existential fight between the democratic world and President Vladimir Putin's aggressive autocracy, is on the verge of drying up.
Republican senators last week blocked a White House request for $106 billion in emergency aid primarily for Ukraine and Israel.
Conservatives said they would refuse the package for the close foreign allies if Democrats and the White House didn't also agree to far-ranging immigration reforms targeting security on the politically sensitive US-Mexican border.
More broadly, the Republican right-wing, led by 2024 presidential candidate Donald Trump, has dramatically soured against Ukraine's cause.
"What's in America's best interest is to accept Ukraine is going to have to cede some territory to the Russians and we need to bring the war to a close," Senator JD Vance, a close Trump ally, said Sunday.
He called White House warnings that allowing Russia to win in Ukraine would put other eastern European countries, including NATO countries, "preposterous."
There should be no "blank check" for Ukraine, Vance said. "You need to articulate what the ambition is. What is $61 billion going to accomplish that $100 billion hasn't?"
In addition to meeting Biden, Zelenskyy is due to address senators and also meet with House Speaker Mike Johnson.