On November 3, voters go to the polls to decide whether Donald Trump remains President of the United States or whether Joe Biden, the Democratic challenger, replaces him.

There are other candidates on the ballot - like the Libertarian Party and the Green Party - but realistically, it's Trump or Biden.

The opinion polls give Biden a strong lead nationally.

On the most authoritative reading, Joe Biden's support is 50.1 of the electorate compared with Donald Trump's 41.8.

But the election won't be decided by the national share. After all, Hillary Clinton won more votes across the country in 2016 than Donald Trump did.

The American system depends on the "electoral college" in which each state has a certain number of "electors".

Bigger states like New York, California, Florida and Texas have more weight when the college convenes in December.

This means that the election will be decided in a few "battle ground" states which switch between Democrat and Republican.

Mr Trump triumphed in 2016 by winning blue-collar northern states Pennsylvania, Ohio, Michigan, Wisconsin, Iowa as well as in Florida.

The bad news for Mr Trump this time is that he trails substantially in swing states including Florida (and if he loses in Florida, his chances of retaining the presidency take a dive).

Remember the well-worn political saying: "The only poll that matters is the one on election day."

Polls can't account for last minute swings as people's minds are concentrated.

There may also be reluctant Trump voters - people who don't like him but who will swallow their distaste and vote for him as "the devil they know".

Polling experts have noticed the phenomenon where pre-election opinion polls have sometimes understated the actual performance of the party of the right.

Pollsters refer to "shy Tories" or "reluctant Republicans" - voters who said they weren't going to vote for the right-wing party in Britain or the US but who then did.

Remember that the Australian punditocracy were surprised by Scott Morrison's victory last year.

Just as in every other aspect of life, the pandemic is present and central.

Committed voters won't change their view but there are signs that some independents may do so because of "Trump's mismanagement of the U.S. response to the coronavirus pandemic", according to Rachel Bitecofer who wrote "The Unprecedented 2106 Presidential Election".

"What was a 13-point advantage for Trump among independents in the YouGov/Economist tracking panel of registered voters in March is currently a 9-point Biden advantage in their most recent poll - a total swing of 22 points."

Joe Biden is portrayed as the "healer in chief". His pitch boils down to: "I'm not Trump and I offer a return to decent American values".

"Our country is hurting, our country is broken, and President Trump is standing there with matches, just flicking them on this tinderbox that we're in right now," Mr Biden said in a speech in Philadelphia.

Expect to see a lot of joint appearances with former president, Barack Obama and with Republicans who have no time for Mr Trump (though Hillary Clinton did that in 2016 but little good did it do her).

There's an old adage in US presidential elections: When you have a record to run on, you make it about yourself. And when your record is terrible, you make it about your opponent.

Mr Trump (74), with COVID-19 and the economy playing terribly for him, is likely to point to Mr Biden's even greater age, perhaps obliquely - he calls him "Sleepy Joe".

Mr Biden will be 78 when and if he moves into the Oval Office. As a boy he stuttered and this can come across now as hesitancy and dithering.

If he sounds confused in a presidential debate, the Trump campaign might well pick up on it.

Mr Trump may well depict Mr Biden as being a socialist in contrast to his own credentials as an avowed capitalist.

There are two views.

One view is that the outrage over the killing of George Floyd at the hands of a white policeman, and all the following Black Lives Matter protests, plays badly for Mr Trump.

Federal officers in military camouflage continue to confront protesters in Portland, Oregon. The Democratic mayor of Portland was himself tear-gassed.

On this view, concerns over civil rights, particularly those of black people, will persuade people to vote against Mr Trump.

The other view is that continuing pictures of riot on the evening news will push wavering voters back into the Trump camp, particularly in the northern industrial states which Trump won in 2016.

The Trump campaign has accused Joe Biden of wanting to "defund the police". It isn't true but the charge may stick.

In his recent memoir, Malcolm Turnbull wrote: "Murdoch's Fox News' relationship with Trump is like that of a state-owned media of an authoritarian government."

That may be over-stating it and Mr Turnbull has an axe to grind with one-time Australian citizen Rupert Murdoch but nobody doubts that the full force of News Corp will be turned on Joe Biden.

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Fox News has the two most watched shows on cable news. It's true that their nightly audiences are barely one per cent of the population, but Fox can set an agenda.

If it focuses on Mr Biden's age, implying senility, it may have resonance.

No. Atmospheres and attitudes morph in the heat of an election.

But whatever the polls say now, it is too soon to write off Mr Trump.