In any other year in US politics, a former vice president with years of experience would have possibly the best shot at the getting the Democratic presidential nomination.

But 2020 is unlike any other year.

Facing in Donald Trump - a Republican incumbent who thrives on his outsider status, Biden's decades-long Democratic resume could prove more of a hindrance than a help.

Biden has consistently led the Democratic pack in national polls, but has encountered tough competition from more progressive wings of the party, personified by Senators Bernie Sanders and Elizabeth Warren, both of whom have promised sweeping institutional changes and are popular among young voters, and a former mayor from the Midwest, Pete Buttigieg, who holds himself up as a moderate.

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Biden, 77, was born in working-class Scranton, Pennsylvania, and has made his nickname, "Middle Class Joe", a mainstay of his campaign. Some observers say his appeal among white working-class voters in the Midwest, the same region that helped put Trump in office in 2016, might be the biggest threat to Trump's reelection.

Biden, who served two terms as vice president under the country's first African-American president, Barack Obama, is also popular among black voters - especially older ones - who make up around 24 percent of the Democratic primary electorate.

Solid support among African Americans

While his Democratic competitors have struggled to appeal to black voters, analysts say African Americans have long been a pillar of support for Biden, especially in his home state of Delaware, which is 38 percent black, and where he served as a US senator for nearly four decades.

Biden says he was inspired to run, at least in part, to correct the racial injustice of the era. In his campaign launch video, he said the last straw was Trump's response to a white supremacist rally in Charlottesville, Virginia, in 2017, during which a neo-Nazi rammed his car into a group of anti-racist protesters, killing 32-year-old Heather Heyer.

At the time, Trump said there were "very fine people on both sides" of the protests.

Biden attacked the president for "assigning moral equivalence between those spreading hate and those with the courage to stand against it".

"In that moment, I knew that the threat to this nation was unlike any I had ever seen in my lifetime," Biden said in the video. "We are in the battle for the soul of this nation."

Biden's commitment to racial justice has not gone unquestioned, however. His Democratic challengers have noted on the campaign trail his key role in the passage of a crime bill in 1994 that mandated harsher sentences for crack versus powder cocaine offences and disproportionately affected minority offenders.

Biden has since released a plan to restructure the criminal justice system and undo many of the 1994 crime bill's more controversial elements.

Also coming back to haunt Biden in the area of race relations - old boasts about his ability to work with segregationists when he was a US senator in the 1970s and about receiving an award from notorious Alabama governor George Wallace in the 1980s.

The 'touchy-feely politician'

With a record in elected office that goes back nearly half a century, Biden brings other baggage with him as well.

Twice before, he has sought the Democratic nomination. The first time, in 1987, he dropped out of the race early following charges that he plagiarised the phrases of other politicians in his speeches. The second time, in 2008, he ended his bid after a poor performance in the Iowa caucuses, and later joined the Obama slate as the nominee for vice president.

His interactions with women over the years have also dogged Biden. Eight women have accused him of touching them inappropriately or invading their personal space in ways that made them feel uncomfortable. None of them have said his behaviour amounted to sexual harassment or assault.

In response, he released a two-minute video in which he said he would try to do better moving forward, but later said he's "not sorry for anything that I've ever done".

Critics claim Biden showed his true colours in his role as chairman of the Senate Judiciary Committee in 1991, when he allowed his colleagues to attack Anita Hill for her allegations that Clarence Thomas, then a nominee for the Supreme Court, sexually harassed her. In recent years, Biden has said he believed Hill's charges all along and apologised for her treatment.

"She did not get a fair hearing," he told ABC's Good Morning America in April 2019. "She did not get treated well. That's my responsibility."

Biden listening while former Iowa Governor Tom Vilsack speaks at a stop on Biden's 'No Malarkey!' campaign bus tour in Iowa [File: Brian Snyder/Reuters]

Impeachment Imbroglio

If he ends up facing Trump in the November general election, Biden is likely to face the most intense criticism over more recent events, however. Much to his dismay, the Democrat found himself at the centre of the impeachment inquiry into Trump's dealings with Ukraine.

The entire impetus for the inquiry was a phone call between Trump and Ukrainian President Volodymyr Zelenskyy during which the US president urged his counterpart to investigate an allegation that in 2016 Biden pressured Ukrainian authorities to shut down a probe that could implicate his son, Hunter Biden, who at the time was on the board of a Ukrainian gas company called Burisma.

Democrats in Congress say Trump abused his authority by conditioning hundreds of millions of dollars in military aid to Ukraine on that investigation, then obstructed Congress when it began investigating the exchange.

So far, Trump and his Republican supporters have not presented any evidence of wrongdoing by the Bidens, both of whom have said they did nothing wrong. Trump was acquitted of the impeachment charges by the Republican-controlled Senate in February.

Biden initially reserved judgement on impeachment, but quickly changed his tune and called for the president's removal from office.

"In full view of the world and the American people, Donald Trump has violated his oath of office, betrayed this nation and committed impeachable acts," Biden said.

Foreign policy: Complete reversal

On the campaign trail, Biden often speaks about the foreign policy credentials he earned during his time in the Senate and the White House. Biden served as the highest-ranking Democrat on the Senate Foreign Relations Committee for 12 years and was involved in foreign policy during his eight years as vice president.

Saying that Trump's foreign policies have done irreparable damage to the US, Biden has promised a complete reversal if elected president.

"If we give Donald Trump four more years, we'll have a great deal of difficulty of ever being able to recover America's standing in the world and our capacity to bring nations together," he said. "I think it'd be catastrophic to our national security and to our future. We can't let it happen."

The travel ban on several majority Muslim countries would end under a Biden presidency, as would US support of the Saudi war in Yemen. The continuing conflicts in Afghanistan and the Middle East would also be reassessed, Biden has promised.

In 2002, in the wake of the September 11 attacks, Biden voted in favour of a congressional resolution that gave George W Bush broad power to go to war with Iraq based on since-refuted claims that President Saddam Hussein was building an arsenal of weapons of mass destruction. He has since backtracked from that position.

During the third Democratic debate in 2019, Biden said he "never should have voted to give Bush the authority to go in and do what he said he was going to do."

Joe Biden and his son Hunter Biden attend an NCAA basketball game between Georgetown University and Duke University in Washington [File: Jonathan Ernst/Reuters]

Healthcare and Immigration

Biden has criticised the Medicare for All plans being pushed by Sanders and Warren as a misguided effort to dismantle the Affordable Care Act (ACA), Obama's signature healthcare law. Instead, Biden has promised to "build on" the act, popularly known as Obamacare, by adding a public option that would leave the current private insurance system in place.

His healthcare plan, estimated to cost $750bn over 10 years and paid for partly by higher taxes on the wealthy, would let people enrol in a paid government healthcare plan as an alternative to private insurance. The proposal also would expand the ACA's subsidies for private policies, making them more generous and extending them to more people.

In another contrast with his progressive challengers, Biden has said he would roll back many of the Trump administration's immigration policies - including a policy that forces asylum seekers to wait in Mexico while their immigration cases are being heard, funding for a wall along the US-Mexico border, and the separation of families being held for immigration violations - but he has stopped short of supporting the idea of decriminalising irregular border crossings, which some Democrats have said they support.

"Joe Biden understands the pain felt by every family across the US that has had a loved one removed from the country, including under the Obama-Biden administration," his website says, "and he believes we must do better to uphold our laws humanely and preserve the dignity of immigrant families, refugees and asylum seekers."