Joe Biden has said that US President Donald Trump's pressure on Ukraine to cede territory to Russia amounts to "modern-day appeasement".
In his first post-presidential interview with the BBC's Today programme, Biden said he worried that relations between the US and Europe were eroding under Trump, with NATO member nations reconsidering whether Washington can be trusted.
"Europe is going to lose confidence in the certainty of America and the leadership of America," Biden told the BBC.
The continent's leaders, he added, were asking: "'Can I rely on the United States? Are they going to be there?'"
Of special concern, Biden said, was the administration's proposal to let Russia keep some Ukrainian territory in an effort to strike a peace deal.
"It is modern-day appeasement," Biden said.
Biden said Trump's lurid argument with Ukrainian President Volodymyr Zelenskyy in the Oval Office in February was "beneath America."
"I don't understand how they fail to understand that there's strength in alliances," Biden said of the Trump administration on Monday.
The term "appeasement" refers to former British Prime Minister Neville Chamberlain's negotiations with Adolf Hitler in the 1930s as he moved to annex and take over areas bordering Germany ahead of the Second World War.
Chamberlain notoriously proclaimed the resulting deal as a harbinger of "peace for our time" in September 1938.
Nazi Germany invaded Poland less than a year later, thus beginning what would become the most devastating conflict Europe has ever witnessed.
Trump claimed on the campaign trail that he could end the war started by Russia's full-scale invasion in mere days, and has long dismissed the conflict as a waste both of lives and of American taxpayer money.
But in office, his approach to negotiating a halt to the fighting has been erratic.
Early in his presidency, he ordered a pause in American aid to Ukraine before resuming it.
Last week, his administration signed an agreement with Kyiv granting the US access to Ukraine's vast mineral resources — a return on investment, Trump suggested, that could clear the way for more US aid to Ukraine.
Trump has also said that Crimea, which was illegally annexed by Russia in 2014, "will stay with Russia", apparently dismissing Ukraine's fundamental demand that Russia return all territory it has seized since it first attacked the country.
Let history judge
Biden also told the BBC that Trump's statements about acquiring Panama, Greenland and Canada have bred distrust of the US in Europe.
"What president ever talks like that?" Biden said. "That's not who we are. We're about freedom, democracy, opportunity — not about confiscation."
He also said it was a "difficult decision" to leave the 2024 presidential race four months before the November 2024 election day to allow former Vice President Kamala Harris to challenge Trump instead of him.
But he also insisted that stepping back earlier, as some critics suggest he should have done, would have made no difference.
Asked about Trump's triumphant celebration of his first 100 days in office, meanwhile, Biden replied that it is for history to judge his successor.
"I don't see anything that was triumphant," he said.
