Since then, a series of stunning events have further up-ended convention.

It is, of course, too early to say definitively.

But some things can be said. Firstly, the polls do not indicate any closing of the gap with Joe Biden; in fact the opposite.

The most respected poll-trackers put Mr Biden on 52 per cent support from likely voters against Mr Trump's 42 per cent, the biggest lead by the Democrat since July.

Mr Trump has not turned the election round.

If the thought was he might emerge chastened from severe illness and able to relaunch his campaign, it hasn't happened. If anything, his lashing out at opponents, and even allies, has increased.

Republicans may regret that a chance was missed.

Under the American system, the winner needs to succeed in a few states which swing one way or the other.

The states send representatives to vote in the Electoral College where the decision is made and a switch from Trump last time to Biden this time in this small number of swing states would change the result.

In 2016, Hillary Clinton won more votes across the country but they didn't translate into votes in the Electoral College.

Nate Silver, who runs the FiveThirtyEight polling site and who is widely respected and seen as non-partisan says: "After a couple of strong polls for Joe Biden in Pennsylvania - the state that's currently most likely to decide the election - Trump now trails there by five or six points.

"He's down by about seven points in Michigan and Wisconsin, meanwhile.

"Those states, along with Minnesota, Maine and New Hampshire - where Biden has also polled strongly lately - suggest that Biden is winning back some of the Obama-Trump white working-class voters who flocked to Trump four years ago."

It isn't. There are routes to victory for Mr Trump if he wins in particular combinations of states, but it is unlikely. His route is uphill.

As Mr Silver puts it: "To be clear, none of this means that Trump's chances are kaput. As of this writing, our forecast still gives him around a 21 per cent of winning the Electoral College. That's not great, but it's a lot better than zero."

The atmosphere is getting uglier.

After the left-wing violence in Portland, Oregon, there is a threat of right-wing violence.

The police foiled a plot to kidnap Michigan's Democratic governor. Separately, seven people linked to a paramilitary group called the Wolverine Watchmen were charged with planning to storm the state's assembly and create a "civil war."

The two groups trained together and planned "various acts of violence," according to the state police.

It is not clear how violence or the threat of violence plays out in voters' minds.

In the past, research has indicated that race riots push white voters to the right.

But would right-wing, white violence (or the threat of it) push more voters towards Mr Trump or away from him?

Would voters see him as the promoter of chaos or the strong man who can bring order?

Perhaps both, with different groups reacting differently. Mr Trump's failure to condemn white supremacy in the first debate might play well with his core but really badly everywhere else.

Mr Trump has repeatedly questioned whether the election will be fair, and thereby undermined its legitimacy.

Without any evidence, he says postal voting leads to fraud.

If he loses narrowly, he may refuse to leave office. He may claim victory even though votes are yet to be counted.

He might contest a result in the courts and the challenge would probably end up in the Supreme Court which might by then have a 6-3 Republican majority.

In the United States, Supreme Court judges are appointed and the dominant political party in the Senate chooses according to its politics. That is currently the Republican Party.

A "liberal" on the court has just died and the Republicans want her replaced with a "conservative" before the election.

We simply don't know if the infection has cleared. Even if it has, the after-effects of COVID-19 can be draining and debilitating.

If he is suddenly taken ill again, there are procedures under the Constitution (Amendment 25) for power to be transferred (procedures that were made ready when Ronald Reagan was shot in 1981).

The Democrats are also questioning Mr Trump's mental state, what the Democrat speaker of the House of Representatives, Nancy Pelosi, called his "altered state".

Earlier this week, Mr Trump, who does not drink, tweeted nearly 50 times within two hours.

Some of the tweets were in capital letters with mis-spelt words.

Democrats are proposing a special bipartisan panel to determine a president's fitness for office.

This is unlikely to happen and has the mark of pure politics.

We'll find out after November 3 but all the indications are it has transformed the campaigns - but not in Mr Trump's favour.