President Trump's recent jab at Bernie Sanders, calling him "a communist," was meant as an insult. But the 2020 Democratic front-runner and Vermont senator might not have taken it that way.

In 1972, Sanders, then a gubernatorial protest candidate for the socialist Liberty Union Party, visited an alternative high school in Rutland, Vermont, to give his campaign pitch. During a question-and-answer session, Sanders, then 31, brushed off accusations of being a left-wing radical.

"I don't mind people coming up and calling me a communist," Sanders said. "At least, they're still alive."

On the night of the Super Bowl, Trump said "communist" was the first word that came to his mind when he thought of Sanders in an interview by Fox News's Sean Hannity.

“I think he’s a communist,” Trump said. “Look, I think of communism when I think of Bernie. You could say socialist, but didn’t he get married in Moscow? That’s wonderful. Moscow’s wonderful.”

Trump was then corrected by Hannity, who explained that Sanders only honeymooned in the Soviet Union in 1988.

Although Sanders has refrained from self-identifying as a communist, his ties with far-left Marxist groups go back decades.

The Washington Examiner reported last May on his ties with far-left political parties such as the Socialist Workers Party. During his time as mayor of Burlington, Vermont, he littered his office with newspapers and pamphlets from revolutionary organizations.

In 1980 and 1984, Sanders endorsed SWP presidential candidates Andrew Pulley and Mel Mason. Their presidential platforms included promises to dismantle the entire U.S. military and nationalize most industries.

Sanders was later investigated by the FBI concerning his ties to the SWP, although charges were never brought.

On Monday, the Washington Post reported that in 1983, Soviet Embassy First Secretary Vadim Kuznetsov congratulated Sanders in a letter for his reelection as mayor of Burlington. Kuznetsov, a leader of the Soviet's spy outfit, had just attended a conference in Sanders's city a few days earlier.