Despite being gaffe-prone, getting up in years and barely heading out on the campaign trail, Democrat Joe Biden is leading in the polls as the coronavirus epidemic and economic crisis make the November presidential election a referendum on Donald Trump.

The COVID-19 outbreak has stripped Trump of his beloved campaign rallies but he has made the most of his White House pulpit to remain in the public eye.

The 77-year-old Biden, on the other hand, has held few campaign events, spending most of his time since mid-March at home in Wilmington, Delaware.   

Biden's sparse public schedule has minimized the risks of his catching the virus while at the same time reducing his chances of making any faux pas.

And if the polls are any indication, the Democratic candidate's low-key style is paying off. The election website Real Clear Politics has Biden with a 7.7-point lead over Trump nationally.  

Allan Lichtman, a history professor at American University, has correctly predicted the results of every US presidential election since 1984, including Trump's upset 2016 victory.

His 2020 forecast? Biden, president Barack Obama's two-term vice president, will win the November 3 vote.

"This has nothing to do with Joe Biden," Lichtman said in an interview with AFP. "It's not dependent on Donald Trump's personality either. It's based on the record."

The professor bases his predictions on what he calls the 13 "Keys to the White House."

Among them: How strong is the US economy? Is there social unrest? Is the president an incumbent? Is the president charismatic? Is his opponent?

Of this last "key," Lichtman says "Biden doesn't fit that bill." 

"He's a very empathetic, sincere man but he's not inspirational," he said.

- 'Failed presidency' -

In late 2019, Lichtman had Trump in good shape to win re-election.

"What has happened since is he made the colossal mistake of thinking he can talk his way out of the crises that hit the country, the pandemic, the cries for social justice, the economic downturn," Lichtman said. "That doesn't work. And the result is a failed presidency."

With more than 169,000 deaths and over 5.3 million COVID-19 cases, the United States is the worst-hit country in the world with an economy on its knees.

The killing of George Floyd, an African-American man, by a white police officer, triggered a summer of nationwide protests against racial injustice and police brutality.

While Trump's handling of the virus outbreak and the protests has been widely criticized, Biden has been climbing in the polls.

The former vice president has been able to largely sit back and watch events unfold, with the Trump campaign accusing him of "hiding" in his Wilmington basement.

"By his almost reclusive campaign he has maintained the spotlight on President Trump," said Christopher Arterton, professor emeritus of political management at George Washington University.

And Trump's management of the crises facing the country has pushed many independent voters "from undecided to, 'I'm not going to vote for him,'" Arterton said.

Despite Biden's lead in the polls, neither professor is ready to say he has the election locked up, not in these uncertain times and with a candidate as unpredictable as Trump.

"He will do anything, he has no scruples," Lichtman, an avowed Democrat, said of the Republican president.

- 'Wild cards' -

Trump, 74, has suggested that Biden is senile and called him a puppet of the "radical left" who would somehow "hurt God."

There are also three debates scheduled between the two men in September and October which could be the occasion for fireworks.

With Trump largely unable to expand his voter base, the real estate tycoon has been accused of trying to suppress the Democratic vote.

Lichtman said this could pose dangers for Democratic hopes of regaining the White House.

"My big worries about this election are two things that have nothing to do with the keys," he said.

"One is voter suppression. Trump and his enablers are going to make it difficult for people to vote, particularly to vote by mail in a pandemic," Lichtman said.

"And number two, Russian intervention. How effective is their intervention going to be? Because we know Donald Trump not only won't do anything to stop it, he'll welcome it again.

"Those are two wild cards. No system can take that into account."