In an interview with the Guardian from his home base in Burlington, Vermont, Sanders urged the Democratic president to inject more urgency into his bid for re-election. He said that unless the president was more direct in recognising the many crises faced by working-class families his Republican rival would win.

“We’ve got to see the White House move more aggressively on healthcare, on housing, on tax reform, on the high cost of prescription drugs,” Sanders said. “If we can get the president to move in that direction, he will win; if not, he’s going to lose.”

The US senator from Vermont added that he was in contact with the White House pressing that point. “We hope to make clear to the president and his team that they are not going to win this election unless they come up with a progressive agenda that speaks to the needs of the working class of this country.”

Sanders’ warning comes at a critical time in American politics. On Monday, Republicans in Iowa will gather for caucuses that mark the official start of the 2024 presidential election.

Biden faces no serious challenger in the Democratic primaries. But concern is mounting over how he would fare against Trump given a likely rematch between them in November.