America, beware of what Donald Trump will do if you empower him in the midterms – he'll stretch the Constitution to breaking point

He will fire Jeff Sessions and Rod Rosenstein, and with no resistance from Congress, neuter the Mueller inquiry. He will target the rights of minorities, gay people and pregnant women. He will go after the First Amendment protection of a free press

Fasten your seatbelts, citizens of Earth, it’s going to be a bumpy night. Or it isn’t. With the US midterms, the one point of agreement among most pundits is that, so far as the outcome, no one don’t know nuffink.

The opinion polls firmly predict that the Republicans will hold the Senate and lose the House of Representatives. But these days, a concussed goldfish with early onset Alzheimer’s remembers enough not to trust the polls.

What we do know is that Donald Trump’s demented genius for ridiculing political truisms is being tested again. If he holds the House – and as ever, despite the infinite electoral complexities, it’s all about him – he will rewrite Marx’s axiom about the repetitive nature of history.

What happened two years ago was a tragedy. If he beats the odds again, history will repeat itself as a greater tragedy. It will be worse because this time there is no excuse. Those who supported him despite their misgivings in 2016, assuming that the rhetoric was empty posturing and that power would constrain him, have learned otherwise.

Yesterday, as if an example were required, various TV networks and social media sites pulled a campaign ad focusing on the “caravan” of migrants making its pitiable way through central America towards the United States’ southern border. Among these was Fox News. Trump’s trustiest propaganda arm concluded that a Trump commercial was too blatantly racist and dishonest to be screened.

While racial sensibilities may be an even stronger determinant than Trump’s failure so far to crash the golden economy he inherited, there are hundreds of reasons – from the microscopically local to the national and global – why Americans will vote one way or the other. But ultimately these midterms will be interpreted as the referendum on Trump they essentially are.

They will brand America, in its own eyes and the world’s, more indelibly than 2016. That can still be written off as an anomaly. When a presidential election pivots on 30,000 votes spread across a few states, any number of factors are decisive.

If James Comey hadn’t reopened the FBI enquiry into Hillary’s emails, or if she’d bothered to stump in the Rust Belt, or if Trump hadn’t bought off Stormy Daniels, or if whatevs… For the next few hours, you can make the case that it was a freak result which better reflected the vagaries of the electoral college system than the values of the American people.

If they leave both Congressional houses in Republican hands, the last dregs of the benefit of the doubt will glug down the plughole, and into the Trumpian sewer. While America will remain as evenly split as before, the headline verdict will be that it has used democracy – a wretchedly flawed form, admittedly, given the gerrymandering of House of Representative districts and feverish Republican efforts to suppress the black vote – knowingly to endorse a form of fascism-lite.

On the Today programme, Hillary’s running mate Tim Kaine identified this as an existential turning point in the life of the republic. If that sounds melodramatic, imagine what holding the House as well as the Senate might embolden him to do.

He will fire Jeff Sessions and Rod Rosenstein, and with no resistance from a despicably supine Congress, neuter the Mueller inquiry they have refused to defang. He will target the rights of minorities, gay people and pregnant women. He will go after the First Amendment protection of a free press, and dare the Supreme Court he has tilted sharply to the far-right to defy him.

Wholly unshackled, he will stretch the Constitution close to, if not beyond, breaking point. And encouraged by what will be unanimously greeted as epic vindication, he will be even more reckless on the geopolitical stage. He could well withdraw the US from NATO, leaving an already fragile world order in a state of collapse from which it would struggle to recover long after he has gone.

Wherever you may be reading this, be it on a Sheffield tram or in a Welsh tea room in the Patagonian desert, from the savannahs of east Africa to the stilt houses of Manila, you should be livid with resentment that your planet’s future revolves around the idiosyncrasies of a tiny number of strangers in a land far away of which you know too much.

If the race for the House is as tight as anticipated, a few dozen votes in a suburb of Michigan and a few hundred more in the potato-farming Idaho countryside could decide whether Trump spends the next two years raining mayhem on us all, or tied up in chains by Democratic investigations. Such is the warped reality of a world that hasn’t begun to rebalance itself since the Soviets slipped off the see-saw.

Then again, with turnout at a historical high, the race might not be tight at all. The exit polls could point to a Democratic wave to sweep away Republican control of the Senate as well as the House, in which event we can ditch the octuple espressos for a hot milky drink. Or they might point towards the other extreme, in which case it’s triple hemlocks all round, and a very deep sleep indeed. No one knows nuffink.

But if the opinion polls are accurate, it promises to a long, terrifying vigil to discover whether the United States has shown buyer’s remorse for being sold a distempered pup in 2016, or has chosen to remove what passes for his leash.