People are calling it donald trumps october surprise. but in most respects the us presidents positive coronavirus test is very different to the traditional pre-election bombshell.

Unlike, say, an osama bin laden tape, which came out in october 2004 just days before george w bushs re-election, mr trumps unpleasant diagnosis will not necessarily help him in the polls. his positive result will focus attention on his handling of the pandemic, where he is already suffering from very poor ratings.

Moreover, the fact that he has contracted the disease arguably should not qualify as a surprise. having spoken at many indoor rallies and gatherings during the past few months, and almost always abjuring a mask, mr trump has wilfully ignored his own scientists advice. sooner or later he was more than likely to be exposed to the pathogen.

The question is whether it will compound his already waning re-election prospects. with just 32 days before the election and millions of votes already in the mail mr trump must now spend at least the next two weeks in isolation. that means no rallies and probably no second debate with joe biden, which was scheduled for october 15.

It could also have drastic knock-on effects among white house staff, who work at close quarters and have mostly been reluctant to irritate mr trump by wearing masks at work. a mini-pandemic in the white house or at least a wave of quarantines could badly hinder its normal course of business. if one of americas adversaries wanted to spring a more conventional october surprise, in the middle east, for example, or the south china sea, now might be an opportunistic moment.

On the face of it, mr trumps twist of fate should reinforce what his critics have been saying for most of the year that all americans, including the president, should follow social distancing guidelines.

It has been seven months since mr trump predicted the virus would disappear like a miracle. the us had fewer than 20 infections and no deaths when he said that. since then, mr trump has called virus warnings a hoax, likened it to the flu, said it would be gone by easter, and most recently forecast that the end is in sight. now america has 7.5m infections, including the president and the first lady, melania trump, and more than 207,000 dead.

Moreover americas curve is not flattening. on wednesday, the number of daily deaths once again rose above 1,000. federal scientists, including dr anthony fauci, are warning of a rising infection rate in the coming weeks as the winter flu season sets in.

In other words, mr trumps diagnosis does not help his campaign.

But politics does not always move in straight lines. there are caveats to the expectation that this is bad for mr trumps campaign. the first is we do not know how severely his health will be affected. the white house says the president has mild symptoms. perhaps it will stay that way. the mortality rate for his age group is 5 per cent in countries with good medical systems, which means he has a very high chance of surviving.

The example of boris johnson, britains prime minister, should give anyone pause. he was hospitalised with covid-19 in march after having boasted of shaking peoples hands in hospitals. his battle with the disease brought a wave of public sympathy which boosted his poll numbers for several weeks. he appeared to pay no price for having ignored social distancing advice.

Second, mr trumps fate could bring back the focus on mr bidens age, who, at 77, is just in a higher risk category than mr trump (74).

If nothing else, the timing of this twist underlines that us politics nowadays often feels scripted by netflix screen writers. a lot of things could happen. mr trump could recover quickly and attribute it to some magical cure. he could fall more seriously ill and temporarily hand over the reins to mike pence, the vice-president. or this presidential election could continue to march grimly towards the conclusion that polls have been predicting for months a biden victory amid dangerous claims of fraudulent mail-in ballots.

My own bet is still on the latter. it is hard to believe mr bidens lead is about to miraculously disappear.