That was extremely unusual,” Prokofiev said. “It was particularly striking to me as a Soviet person.”

When he enters the White House next month, Joe Biden will bring nearly half a century of foreign policy experience with him, making him one of the most seasoned envoys ever elected president. “Joe knew the Soviet Union, knows Russia, has experience with [Vladimir] Putin, and understands what’s possible and what’s probably not,” said former senator Bill Bradley, who visited Moscow with him in 1979.

Boasting of those credentials, Biden for a time recalled sitting briefly across from Leonid Brezhnev in the Kremlin in 1979 before negotiations with Alexei Kosygin, the Soviet premier. “Brezhnev looked grey; we didn’t know it but he was already sick and dying. The Soviet president excused himself after introductions and turned the meeting over to Kosygin,” Biden wrote in a 2007 memoir. He repeated the story to Putin four years later.

But Andrei Kozovoi, a historian at the University of Lille and author of a forthcoming biography of the Soviet leader, noted in a detailed look at the delegation that Brezhnev never mentions meeting those US senators in his diaries. Nor does his secretary, or anyone else on the trip.

“Brezhnev was in no meeting that I was in and I was in all the delegation meetings on that trip,” said Bradley. Former senator Carl Levin also confirmed that Brezhnev was not there. Biden’s transition team did not respond to a request for comment.

Biden has faced scrutiny before over claims about his foreign adventures. During the Democratic primary race earlier this year, he repeatedly asserted that he was arrested in apartheid South Africa while trying to visit Nelson Mandela in prison. US newspapers investigated and debunked the story and Biden eventually acknowledged: “I wasn’t arrested, I was stopped. I was not able to move where I wanted to go.”

Brezhnev’s cameo in his memoirs lends a young Biden gravitas. But at the time, said Kozovoi, Biden was just “one tiny little cog in the Carter ‘detente machine’”, sent to Moscow to help allay domestic concerns about the Salt II treaty. Few Soviet officials mention the president-elect in their memoirs, and Soviet press clippings curtly note the senators arrivals in Leningrad and Moscow. Bradley recalled the meeting with Kosygin, which lasted three hours, as substantive, and said the delegates also met with foreign ministry officials and had lunch with a senior military official.

But in those early trips, Biden cultivated a pugnacious style in his meetings with Soviet leaders that became his hallmark. If Donald Trump came to Moscow chasing real estate deals and Bernie Sanders sought to join the peoples of Burlington and Yaroslavl, then Biden’s formative years here were the decades he spent showing he could go toe-to-toe with Kremlin officials on arms control.

It is a role he’ll reprise next month with Putin as the new strategic arms reduction treaty, a deal he helped move through the Senate as vice-president in 2010, is set to expire.

“I’m from Delaware and we have a saying – you can’t shit a shitter,” Biden told Kosygin in 1979, Levin recalled. Asked how it had sounded in Russian, an interpreter said: “You can’t fool a comrade.” Biden apparently liked the phrase to repeat it nearly verbatim – “you can’t bullshit a bullshitter” – during his next trip in 1984.

But he is remembered in Russia as a proponent of detente who sought to bridge the gap between Moscow and Washington even as relations collapsed in the early 1980s. Pessimists say the mutual distrust now may be worse.

“If we had the Biden of the 1970s and 80s [in the White House], people would not be worried,” said Sergey Karaganov, a prominent foreign policy expert who said he had played a minor role in organising trips attended by Biden in the 1980s.

He recalled the impression Biden made then: “American, good-looking, establishmentarian left-of-centre”.

Biden’s appeal is immediately visible in a 1979 television interview that went viral in Russia after his reelection. “I think the prospects for Soviet-American relations are good,” Biden says earnestly before jumping into shop talk on Salt II (it ultimately failed but both sides abided by limits on the number and type of missiles until 1986).

The Soviet invasion of Afghanistan in 1980 sent relations between the White House and the Kremlin into a deep freeze. Biden only returned to Moscow in 1984, joining then-senator William Cohen to bring a private message from Ronald Reagan regarding a “new approach to arms control”.

By all accounts, the two took their mission deadly seriously. Reagan wrote that the two had “been to Russia and are all wrapped up in ‘arms reductions’. I suspect that at least one of them (J.B.) doesn’t believe I’m sincere about wanting them.” Two years later, Reagan and Mikhail Gorbachev seriously discussed eliminating all nuclear weapons during the Reykjavik summit.

Biden returned with a delegation and his son in tow in 1988 to discuss ratification of the international nuclear forces treaty with Gromyko, his Soviet counterpart. The treaty had already been signed. “This was pretty much a well-organised, pre-orchestrated and pre-engineered meeting where everyone watches his language,” Prokofiev, the translator, said. The INF, which in effect banned nuclear missiles that could be launched from the Soviet Union into Europe and vice versa, is one of several key agreements that the US has left under Trump.

Biden’s next big visit to Moscow would not come for another 20 years, by which time Putin had dominated Russia’s politics for a decade and even a reset of relations had soured. The conversation had shifted since the cold war, too, from arms control and military balance to questions about democracy promotion and the economy.

But Bradley said that decades of policy experience were still relevant. “Joe is not manipulatable,” he said, recalling Trump’s meeting with Putin. “If there was a chance for a new relationship with Russia, it really stands a better chance of coming with Biden than with Trump.”

Sizing up Putin in 2011, Biden recalled giving him some straight talk: “Mr Prime Minister, I’m looking into your eyes, I don’t think you have a soul.” (In remarks from 2001 that have aged poorly, George W Bush said he had looked into Putin’s eyes and seen his “soul”.)

“We understand each other,” Putin responded, according to Biden.

But he had also told opposition leaders (and by some accounts Putin himself) that he should not run for a third term.

Several Russian analysts said that had crossed a red line.

“Putin remembers personal attacks,” said Karaganov. “He will never forget that.”