Spewing every cliche in the mid-20th century pro-Soviet vocabulary, Britain’s former opposition leader, Jeremy Corbyn, is on an American tour that includes a chummy “catch up” with Senator Sanders and Representative Rashida Tlaib. 

The main cause that brought the former Labour leader to Washington is solidarity with the WikiLeaks founder, Julian Assange, who is jailed in Britain, awaiting extradition to America for trial on espionage charges. 

Like the blame-America-firsters of his revolutionary youth, Mr. Corbyn is fond of anyone out to harm America. “Wikileaks exposed crimes of US empire,” he tweeted last year. “The perpetrators of these crimes walk free but should be held accountable for the lives and futures they stole.”  

The cause, though, goes beyond just one accused spy. As in the refrain of the old Marxist anthem —  “So comrades, come rally / And the last fight let us face / The Internationale unites the human race” —  Mr. Corbyn is recruiting the likes of Mr. Sanders to his globe-encompassing movement, Progressive International. 

“Progressive International is a coming together of progressive forces around the world,” Mr. Corbyn told the broadcaster Democracy Now. “We’re working very closely with people in Brazil, in Colombia, in Chile, in Peru, in Bolivia, and all over Latin America, as well as many European groups and people in other parts of the world.”

The meeting with Mr. Sanders was “entirely about industrial issues and class politics,” Mr. Corbyn said. “The wave of strikes in Britain, the wave of strikes in France, and the need for the left across the world to be stronger in its anti-austerity politics. Not just to manage our economies but to change them.”

Mr. Sanders is all in with the Marxist terminology. “I was pleased to meet today with former leader of the Labour Party @jeremycorbyn and his colleagues at the @ProgIntl and the @corbyn_project,” he tweeted. “I look forward to working together to build international solidarity toward a future that works for all people.” 

The transatlantic mind-meld sent leftists on Twitter to conjure an alternative reality — a socialist paradise in which, rather than being crushed by Boris Johnson in 2019, Mr. Corbyn is now the British prime minister, and Mr. Sanders, the 2020 primary loser to Joseph Biden, is in the White House. 

“Imagine there’s no country … nothing to kill or die for.” By 1971, when John Lennon wrote that hit paean to Marxist dreams, the USSR was nearing its final demise. Yet, some remained nostalgic for the days of Soviet glory.

One of them, Mr. Corbyn, was making his way up the greasy British political pole, capturing the leadership of the Labour Party in 2015 and using his perch there to spew old Kremlin-inspired slogans.

A sub-genre of 20th century Soviet propaganda was the portrayal of Zionism as the West’s cat’s paw. The campaign was so successful that the United Nations adopted it in a resolution equating the Jewish liberation movement to racism.

As painstakingly documented by the Siberia-born Izabella Tabarovsky, the future Palestinian leader, Mahmoud Abbas, wrote a 1972 Holocaust-denying tract for a Moscow university. The young Palestinian activist’s thesis was a product of an antisemitic-rooted pseudo-scientific branch of Soviet academia dedicated to the anti-Zionist cause. Its targets in the West were the likes of Mr. Corbyn, who enthusiastically became a flag bearer of the hate-Israel camp. 

In 2014 Mr. Corbyn traveled to Tunisia to glorify the legacy of Black September terrorists who had massacred Israeli athletes at the 1972 Munich Olympics. Hezbollah and Hamas were his “friends,” he later said. Following his 2019 electoral loss, Labour suspended Mr. Corbyn’s membership for failing to curb antisemitism in the party ranks. 

In contrast, the Jewish-American Mr. Sanders often waxes nostalgically about his stay, as a young man, at an Israeli Kibbutz, albeit one that once celebrated Stalin. The Vermont senator, however, underplays his 1988 honeymoon in the USSR and the praise he heaped on the Soviet paradise at the time.   

As a presidential candidate Mr. Sanders wrote an essay on antisemitism, which included lines like “the struggle against anti-Semitism is also the struggle for Palestinian freedom.” Mr. Corbyn praised that essay, tweeting that he was committed to be Mr. Sanders’s “ally in the fight” against antisemitism.

Professing affinity for Israel, though not for any of its recent leaders, Mr. Sanders nevertheless recruited an anti-Israel activist, Matt Duss, to be his foreign policy adviser. The senator is a leader of the congressional “squad” — a new generation of socialist Democrats, including Ms. Talib, a shockingly coarse critic of Israel. 

Messrs. Corbyn and Sanders “traffic in the same old recycled bankrupt ideas that those of us who grew up in the socialist bloc have burned into our memory,” Ms. Tabarovsky told the Sun.

Their younger followers in academia, entertainment, and politics, she says, are wiping out of their memories “75 years of failure and destruction for hundreds of millions of people,” including Jews, who forget “what happened the last time somebody tried to sell them on a universalist socialist vision.”