Bernie Sanders once contemplated a primary challenge to Barack Obama in 2012, before a top Democratic senator intervened and pleaded with him not to do so, according to a new report.

The Vermont senator is now seeking the 2020 Democratic nomination, but he apparently once considered making his first presidential run a longshot bid to take on the most recent Democrat to occupy the Oval Office — and one who remains one of the most popular figures in that same party.

The contemplations were reported in The Atlantic, which claimed that Mr Sanders was convinced not to mount that run by Harry Reid, the retired Nevada senator who was once the Senate majority leader.

According to that report, Mr Sanders at the time discussed a potential run with fellow Vermont senator Patrick Leahy, who then notified the former president’s reelection campaign manager, Jim Messina.

They were “absolutely panicked”, that former campaign manager said, because “every president who has gotten a real primary has lost a general [election].”

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The Atlantic reports that Mr Reid called Mr Sanders on at least two occasions. Mr Sanders ultimately did not seek the nomination.

The new report once again highlights the reportedly fraught relationship between Mr Sanders and Mr Obama, who separate reports have indicated has considered the option of stepping in during the primary if it appears as though Mr Sanders might win.

Despite the apparent unease from establishment democratic figures, Mr Sanders is now the leading candidate in the 2020 presidential race, after strong showings in both early nominating states to have voted so far, Iowa and New Hampshire.