If the coronavirus had not already posed a threat to civil discourse in the US, the latest flashpoint in American racial politics makes this presidential campaign potentially one of the most incendiary in history.

COVID-19 and Minneapolis may very well form the nexus within which the 2020 campaign will unfold. Trump's critics have assailed his handling of both and questioned whether he can effectively lead the country in a moment of crisis.

And yet, he may not be any more vulnerable heading into the election.

As the incumbent, Trump certainly faces the most immediate challenges. Not since Franklin Roosevelt in the second world war has a US president presided over the deaths of so many Americans from a single cause.

The Axis powers and COVID-19 are not analogous, but any presidency is judged by its capacity to respond to enemies like these. With pandemic deaths now surpassing 100,000, Trump's fortunes will be inexorably tied to this staggering (and still rising) figure.

Worse, the Minneapolis protests are showing how an already precarious social fabric has been frayed by the COVID-19 lockdowns.

Americans have not come together to fight the virus. Rather, they have allowed a public health disaster to deepen divisions along racial, economic, sectional and ideological lines.

Trump has, of course, often sought to gain from such divisions. But the magnitude and severity of the twin crises he is now facing will make this very difficult. By numerous measures, his is a presidency in crisis.

And yet.

Trump, a ferocious campaigner, will try to find ways to use both tragedies to his advantage and, importantly, makes things worse for his challenger.

For starters, Trump did not cause coronavirus. And he will continue to insist that his great geo-strategic adversary, the Chinese Communist Party, did.

And his is not the first presidency to be marked by the conflagration of several US cities.

Before Minneapolis, Detroit (1967), Los Angeles (1992) and Ferguson, Missouri (2014) were all the scenes of angry protests and riots over racial tensions that still haven't healed.

And in the 19th century, 750,000 Americans were killed in a civil war that was fought over whether the enslavement of African-Americans was constitutional.

Trump may not have healed racial tensions in the US during his presidency. But, like coronavirus, he did not cause them.

Not unhappily for Trump, Minneapolis is a largely Democratic city in a reliably blue state. He will campaign now on the failure of Democratic state leaders to answer the needs of black voters.

Trump will claim that decades of Democratic policies in Minnesota - including the eight years of the Obama administration - have caused Minneapolis to be one of the most racially unequal cities in the nation.

In 2016, Trump famously asked African-Americans whether Democratic leaders have done anything to improve their lives.

"What do you have to lose by trying something new, like Trump?"

He will repeat this mantra in the coming months.

It also certainly helps that his support among Republican voters has never wavered, no matter how shocking his behaviour.

He has enjoyed a stable 80 per cent approval rating with GOP voters throughout the coronavirus crisis. This has helped keep his approval rating among all voters steady as the pandemic has worsened, hovering between 40 and 50 per cent.

These are not terrible numbers. Yes, Trump's leadership has contributed to a series of disasters. But if the polls are correct, he has so far avoided the kinds of catastrophe that could imperil his chances of re-election.

Biden should be able to make a good case to the American people at this moment that he is the more effective leader.

But this has not yet been reflected in polls, most of which continue to give the Democrat only a lukewarm advantage over Trump in the election.

The other problem is that the Democratic party remains discordant. And Biden has not yet shown a capacity to heal it.

Race has also long been a source of division within Biden's party. Southern Democrats, for instance, were the key agents of slavery in the 19th century and the segregation that followed it into the 20th.

After the 1960s, Democrats sought to make themselves the natural home of African-American voters as the Republican party courted disaffected white Southern voters. The Democrats largely succeeded on that front - the party routinely gets around 85-90 per cent of black votes in presidential elections.

The challenge for Biden now is how to retain African-American loyalty to his party, while evading responsibility for the socio-economic failures of Democratic policies in cities like Minneapolis.

He is also a white northerner (from Delaware). Between 1964 and 2008, only three Democrats were elected president. All of them were southerners.

To compensate, Biden has had to rely on racial politics to separate himself from his primary challenger - Bernie Sanders struggled to channel black aspirations - and from Republicans. And this has, at times, caused him to court controversy.

In 2012, he warned African-Americans that then-Republican presidential candidate Mitt Romney would put them "all back in chains". And just over a week ago, he angered black voters by suggesting those who would support Trump in the election "ain't black".

Biden is far better than Trump on racial issues and should be able to use the current crises to present himself as a more natural "consoler-in-chief", but instead, he has appeared somewhat flatfooted and derided for being racially patronising.

The opportunities COVID-19 and the Minneapolis unrest might afford his campaign remain elusive.

America enters the final months of the 2020 campaign in a state of despair and disrepair. The choice is between an opportunistic incumbent and a tin-eared challenger.

But the US has faced serious challenges before - and emerged stronger. Neither the civil war in the 19th century or the Spanish flu pandemic in the early 20th halted the extraordinary growth in power that followed both.

Moreover, the US constitution remains intact and federalism has undergone something of a rebirth since the start of the pandemic. And there is a new generation of younger, more diverse, national leaders being forged in the fire of crisis to help lead the recovery.