Biden -- whose backing for Israel in the face of civilian casualties had riled the left of his Democratic Party months before elections -- has been incensed that Netanyahu has rejected appeals to stay out of Rafah, the southern Gaza city where the United Nations says some 1.4 million displaced Palestinians are sheltering.
Biden administration officials initially saw Netanyahu's vows to attack Rafah as rhetorical. But in talks with the prime minister, including a visit last week by Secretary of State Antony Blinken, US officials have been convinced that Netanyahu is serious.
Biden, in an interview with CNN on Wednesday, vowed to stop supplying bombs and artillery shells if Israel goes ahead in Rafah, after his administration confirmed it had already halted a shipment of thousands of bombs.
Biden, who last spoke to Netanyahu on Monday, has made his case on Rafah "repeatedly and straightforwardly," National Security Council spokesman John Kirby said, adding that the invasion was now "a choice that Israel will have to make."
"It's one we hope they don't," Kirby said.
Netanyahu -- who has vowed to eliminate Hamas, which carried the deadliest ever attack on Israel on October 7 -- publicly brushed aside Biden's warnings.
"If we have to stand alone, we will stand alone," he said.
Israel's ambassador to Washington, Michael Herzog, said that while he had "full admiration" for Biden, the threat to withhold US weapons was "unacceptable" and "sends the wrong message" to Israel's adversaries.
Biden's Republican rival in November elections, former president Donald Trump, accused Biden of siding with Hamas.
But Trump's relations have also been strained with Netanyahu, who swiftly recognized Biden's victory in the 2020 election which Trump refused to concede.
- Another brawl for Bibi -
Fights with Washington are familiar terrain for the hawkish Netanyahu.
Israel's longest-serving prime minister, who knows the United States intimately from years living in his country's primary ally, clashed bitterly with the last two Democratic presidents, Bill Clinton and Barack Obama.
Netanyahu openly campaigned alongside Obama's Republican rivals against his nuclear diplomacy with Iran, leaving lasting resentment among many Democrats.
But Biden as Obama's vice president was known internally for advocating holding the Israelis close and expressing concerns privately.
Biden's approach comes both from his history with Israel and the importance he attached to personal relationships.
Biden has often spoken of traveling as a young senator to Israel shortly after the 1973 Yom Kippur War and being briefed by a chain-smoking prime minister Golda Meir.
At a 2010 event, Biden said his father, horrified by the Holocaust, said his love of Israel "began in my gut and went to my heart" and that his father vocally supported the creation of the state of Israel.
In the same remarks, Biden described Netanyahu as a "close, personal friend" for decades, with Biden having met the future Israeli leader, known by his nickname Bibi, when he was a young diplomat in Washington.
In a later speech, Biden described a photograph he once gifted to Netanyahu, saying he inscribed on it, "Bibi, I don't agree with damn thing you say, but I love you."
- 'The bear-hug didn't work' -
Allison McManus, managing director for national security and international policy at the left-leaning Center for American Progress, said that whatever the two leaders' history, their interests were "completely at odds."
"This is not necessarily a personal friendship that is somehow going to eclipse the strong political interests that each of these leaders has," she said.
"This is a moment where I think Biden sees that the bear-hug didn't work. The strong, stern words didn't work," she said. "Withholding the weapons is the biggest tool of influence that the US has."
But she noted that Biden made a threat rather than simply stopping the weapons.
In doing so, Biden is "leaving the door for Netanyahu to pull back from Rafah," she said.
