The US President has warned against giving Vladimir Putin what he called the "greatest Christmas gift".
He was talking about Congress still failing to approve billions of dollars in aid for Ukraine.
Biden told President Volodymyr Zelensky the US will support Ukraine's war effort "for as long as we can", in a change from when he used to say "for as long as it takes".
Zelensky took his fight to Washington in an attempt to convince them himself.
"Today, Ukraine's freedom is on the line," said Biden.
Twelve days before Christmas, Ukraine's president arrived back in Washington.
As his country plunges into a dark winter, he needs American dollars to keep fighting Russia.
If it was just President Biden to convince, Zelensky wouldn't have needed to come so far.
"If we don't stop Putin, it will endanger the freedom of everyone, almost everywhere," Biden added.
"Ukraine can now tackle the Russian dictatorship," Zelensky responded.
To make that a reality, the White House has proposed a huge funding injection for Ukraine - US $60 billion, on top of the $75 billion in cash and equipment it has already given.
But it first needs approval from Congress, where Zelensky held meetings with lawmakers on Wednesday morning.
"If we lose, Putin wins, and this would be very, very bad for the United States," said US Senator Chuck Schumer.
But what would be "worse" - according to some Republicans who are holding up the bill - is the immigration crisis in the US.
They're refusing to pass any funding until the President does more to secure the southern border with Mexico.
"We had 12,000 illegal crossings one day alone last week, on Wednesday," said US House Speaker Mike Johnson.
Zelensky's arrival was a far cry from the hero's welcome he first received in the US.
This is his third trip to Washington since the war broke out.
He arrives at a time when it's not just US politicians questioning how much money is sent to Ukraine - it's also the general public.
"When things are first in the news, and it's the main thing, people pay a lot of attention," said Professor Hans Noel from Georgetown University's Department of Government.
"Generally, Americans are supportive of Ukraine, but after a while [they] think: 'haven't we done this already?' And it starts to get crowded out by other events."
Zelensky now heads home in the hope his journey was worthwhile.
Meanwhile, his closest ally, the US, is still deciding if it will help Ukraine continue to defend itself.Meanwhile, his closest ally, the US, is still deciding if it will help Ukraine continue to defend itself.
