The Republican leader of the US House of Representatives on Tuesday blocked war aid for Ukraine, ignoring President Joe Biden's plea that passing the bill was vital for standing up to "Russian dictator" Vladimir Putin.
Speaker Mike Johnson, who works closely with Mr Biden's likely challenger in the November election Donald Trump, told reporters he has no intention even of allowing a vote on the bill.
"I certainly don't," he said.
The bill was approved in the Senate earlier Tuesday. It includes $95 billion in funding, mostly for the security of pro-Western Ukraine, as well as for the top US strategic priorities of Israel and Taiwan.
At the White House, President Biden said that helping US allies - and particularly coming to the aid of Ukraine as it struggles to fend off a two-year Russian invasion - is a fundamental responsibility.
"History is watching," said Mr Biden, repeating the phrase five times in televised remarks. "Supporting this bill is standing up to Putin. Opposing it is playing into Putin's hands," the Democrat added.
President Biden also lashed out at Donald Trump after the former president encouraged Russia to attack NATO members who failed to meet financial commitments.
"For God's sake, it's dumb. It's shameful. It's dangerous. It's un-American," Mr Biden said, saying that twice-impeached Mr Trump viewed the Western military alliance as a "protection racket".
"No other president in our history has ever bowed down to a Russian dictator."
Republican maneuvers
US aid to Ukraine has been stalled for months by chaos in Congress, even as Kyiv begs for help to counter increased Russian attacks.
The $95 billion Senate package includes funding for Israel's military and for democratic island Taiwan, but the lion's share - $60 billion - would help Ukraine restock ammunition supplies, weapons and other crucial needs.
It passed easily in the Senate when enough Republicans defied Mr Trump's behind-the-scenes maneuvers.
But Speaker Johnson then said he could not address Ukraine's security without first having strict new measures to stop illegal migration into the United States across the Mexican border.
"We really do owe it to the American people to get control of that border," he said.
In fact, Democrats in the Senate had already worked with Republicans to craft a joint bill which provided the foreign aid, while at the same time imposing the harshest new US border security measures in decades.
That bill was primed for approval in the Senate when Mr Johnson announced it would be killed in the House.
This prompted the Senate to ditch that version and switch to Tuesday's new foreign-aid-only bill - which was once again rejected by Mr Johnson.
'Fundamental dishonesty'
Donald Trump - who dominates the Republican Party despite losing the last election and now facing 91 criminal counts in four separate cases - has pulled the strings in Congress throughout the saga.
He opposes helping Ukraine's fight against Russia, saying he would resolve the war in one day if elected, and he has openly told lawmakers not to pass US border reforms - while campaigning heavily on what he says is a desperate need to fix the border.
President Biden has attacked Mr Trump for using the border issue as a political battering ram.
About the same number of voters in an ABC Ipsos poll on Sunday blamed Republicans (53%), Democrats (51%), but Mr Biden was blamed by 49% for the failure to pass border laws - while only 39% blamed Mr Trump.
One Republican senator, Bill Cassidy, lashed out at his party Tuesday after Speaker Johnson killed the aid bill.
"I'm incredibly frustrated. I'm frustrated because I feel this is a fundamental dishonesty with the American people," he said.
