Joe Biden might appear the most likely Democrat to win the primaries and take on Donald Trump in 2020 – but the 76-year-old politician may be facing his greatest uphill battle yet as he tries to reconcile his past with voters calling for a progressive future.

For each of his political flaws, there seems to be a younger, fresher Democrat lacking similar baggage.

Whereas Mr Biden voted to support legislation the National Rifle Association (NRA) hailed in 1986 as “the law that saved gun rights” in America, Kamala Harris proposed this week a slate of aggressive executive actions on gun control reform that she would take if congress fails to act within her first 100 days in the Oval Office.

Mr Biden’s record also includes longstanding support, dating back to 1999, for the Bankruptcy Reform Act, a bill critics said made it more difficult for students to release college-related debts. Elizabeth Warren, by comparison, recently called for debt-free college and massive student loan cancellations.

A 39-year-old Mr Biden also voted in favour of an amendment allowing individual states to overturn Roe v Wade in 1982, while the 46-year-old Beto O’Rourke speaks eloquently and unabashedly about his support for pro-choice abortion policies, even in his deeply red home state where the issue remains taboo.

“There’s plenty of fodder for all of [Mr Biden’s] opponents to jump on,” Tobe Berkovitz, a professor at Boston University who has spent 30 years as a Democratic political media consultant, told The Independent.

“He is somewhat the frontrunner … and he also has perhaps the most amorphous record because he was in the Senate so long, he was the vice president – so there are going to be plenty of things these campaigns can find as a weakness at the current time in his record.”

Yet as one of the highest-polling Democrats to throw his hat in the ring this season, Mr Biden still remains popular across the country for his brand of centrist politics, and reports indicate he will run on a message of unity and moving the country forward.

Mr Biden says he’s changed his stance on a range of issues – and in many ways he has. Former president Barack Obama tasked him with spearheading the former administration’s efforts surrounding gun control, and he earned an “F” from the NRA. He also was one of the highest-profile Democrats to support marriage equality, before the Supreme Court legalised same-sex marriage in 2015.

He’s previously rebuked his own past in some cases, acknowledging his “regret” over his handling of the Anita Hill hearings in 1991 as chairman of the Senate Judiciary Committee.

“I wish I could have done something – I opposed Clarence Thomas’s nomination, and I voted against him,” he said in a recent statement. “But I also realised that there was a real and perceived problem the committee faced: there were a bunch of white guys.”

Mr Biden seemingly foreshadowed how he might address the controversies from his past in a March speech.

“I’m told I get criticised by the ‘New Left’,” he said. “I have the most progressive record of anybody running for the … anybody who would run.”

Other facets of his past could also seriously diminish his shot in 2020, after multiple women accused Mr Biden in recent months of inappropriate touching along the campaign trail in past years. He has not been accused of sexual assault.

In an op-ed, HuffPost’s Washington bureau chief Amanda Terkel wrote: “Biden is the wrong guy to bear the standard of any party purporting to speak for victims of unaccountable power.

“The newly energised women under the Democratic tent may not want a relic from the pre-woke era to be their standard-bearer.”

Mr Biden also faces a bounty of criticism over his handling of racial issues, including his support for desegregating schools while previously referring to integration as “the most racist concept you can come up with”.

Support free-thinking journalism and subscribe to Independent Minds

When announcing the end of his first presidential candidacy in September 1987, Mr Biden blamed “the exaggerated shadow” of his past mistakes for obscuring “the essence” of his campaign.

He also expressed frustration with “the environment of presidential politics that makes it so difficult for the American people to measure the whole of Joe Biden and not just the misstatements that I have made.”

“There will be many opportunities for me to run for president again,” he said at the time.

Whether that opportunity has already come and gone for Mr Biden, however, will soon be far more evident.