In Britain we are still assuming that we will not wake up on Wednesday to the news that President-Elect Trump is shortly to be installed in the White House. Or the Trump House as he will call it once it’s been redesigned as a building more appropriate to the 21st century.

But of course we said the same about the Brexit referendum in June. There was no way Remain could lose: too much uncertainty; too much financial pain; too much of a step back into a nationalistic world of competing polities. And we were wrong. A majority – admittedly a slim majority – let out a howl of anger about a variety of issues and decided to make the EU the whipping boy for their anguish.

To hell with economic growth and political stability, we were going to leave. Lots of people in the UK decided they had nothing to lose anyway, so backed the destructive course for the sheer hell of it, and maybe Americans will do the same. There comes a point where you’ve gone so low in life that Armageddon looks quite attractive.

When we Remainers (or “Bremoaners” as the “Brexiteers” now like to paint us) woke up on 24 June to the news that the unthinkable had happened and the UK – or parts of it – had voted to leave the EU, the first reaction was one of disbelief. How could a majority of my fellow citizens have voted to turn the clock back in this way?

A young woman on the news summed it up perfectly on that morning. She said she was in a daze, doing the things she normally did, seeing the people she normally saw, but knowing that many of them had voted Leave – something she saw as anathema. She likened them to “zombies”: she thought she knew and understood the people she lived among, but clearly she didn’t.

A chart showing the drop in the pound against the US Dollar in London on 24 June 2016, the day after the referendum. Photograph: Daniel Sorabji/AFP/Getty Images

This was the disbelief phase, and it quickly gave way to anger. How could voters be so dumb? How could they swallow all the Leave lies about giving more money to the NHS? People were never really told what leaving the EU would mean. The fine detail – the question of “hard” v “soft” Brexit, questions about the status of EU citizens already here and British citizens living in the EU, the role of parliament in determining the terms on which we leave – are only now being discussed.

The debate, if it can be called that, in the months leading up to the vote on 23 June was laughably simplistic. An immensely complex decision had been reduced to a binary vote. The referendum was a fiasco and should never have been called. Losing his job as prime minister wasn’t sufficient punishment for David Cameron, who had called the referendum to try to salve wounds in the Conservative party and then led a ham-fisted, directionless campaign to keep us in. He should have been locked up in the Tower of London.

But anger only gets you so far. Thinking back to the referendum, one image stuck in my mind. The day before the vote I’d been shopping in a high street close to where I live in south-west London. I’d noticed a young man with a clipboard – I assumed he was a student at the local university – walking up and down the street handing out leaflets and badges, and talking to passersby. He was campaigning for Remain. One person trying to do something for the cause he believed in.

And I felt guilty, because I had done nothing to try to keep Britain in the EU – a cause in which I passionately believed. I had assumed my fellow zombies would be too sensible to swallow the Leave nonsense and immigrant-scapegoating and vote to quit the EU. I realised that I – and all of us Bremainers/Bremoaners – deserved what I had got. Our arrogance had lost us the referendum.

The neighbourhood in which I live had been festooned with Leave posters. The Leavers really wanted this and were prepared to make public their preference. In sporting parlance, they were up for it. The then Ukip leader Nigel Farage said his supporters would “crawl over broken glass” to get to polling stations to vote to leave the EU, and he was right. Leave may not have had the arguments on their side, but they had all the energy. Remain, who didn’t put up posters or show any passion for their cause, were supine in the face of their rhetoric. “The best lack all conviction, while the worst are full of passionate intensity.” How right Yeats was.

Does all this remind you of anyone? Trump may talk nonsense a lot of the time, but there’s no denying his energy, passion and rhetorical skill. I watched several of the debates involving the Republican hopefuls, and he was incredibly bullish and entertaining. There was no denying he was box office. In an age increasingly suspicious of technocrats, and with people in the “squeezed middle” struggling to stay afloat and looking for simple solutions, Brexit/Trump is an attractive proposition.

All of which led me to the phase I’m now at – believing that I’m as guilty as every other Remainer (except the guy with the clipboard) for the catastrophe of 23 June, and eager to join the battle to rectify the mistake. We had a referendum in 1975 to stay in the forerunner of the EU; we decided to leave in 2016. In my book that makes the referendum score 1-1, and there is still all to play for. I believe (perhaps naively) that once people see the damage leaving would do to the UK economically and politically, sentiment will change.

I will do all I can to help shift that sentiment – writing pro-EU articles, arguing the Remain cause, getting involved in some of the pro-Remain organisations now springing up. We are the insurgents now; we have the passion and the energy. The Leavers are in the ascendant, but defence can be harder than attack if the attackers are determined, as we will have to be.

In this third phase, following denial and anger, I have never felt so energised. I have found a cause in which I truly believe – openness, tolerance, togetherness, economic growth for our common social good. I am even typing this in a T-shirt that displays the 12 stars on a blue background that signify the European Union. I feel I owe it to that student who worked so hard while the rest of us did nothing. He saw the danger of defeat; we arrogantly assumed life would go on as normal. The things that matter in life have to be fought for.

So if Trump does win, it’s your fault. Just as I have to recognise that I am partly responsible for Brexit, so you would have to recognise you are responsible for Trump and Trumpism (or is it Trumpery?).

And for you, as for me, the only response to that realisation is to change your ways and fight. Unlike Brexit, where us Bremoaners have an outside chance of being able to reverse the decision, or at least to argue for a Brexit so soft that you will barely discern what has changed after our exit from the EU, you would be stuck with Trump for four years (unless you find grounds for impeachment, which might indeed be possible). But you still have to fight.

From day one of a Trump presidency, work for the America that is as good as you want it to be. Join campaigning organisations; find (or found!) a political party that reflects your views; get involved in a social group that is working for greater equality and an end to deprivation in your town. You are stuck with Trump, but you can still oppose, negate and eventually destroy Trumpism (assuming the new president doesn’t destroy us all first in his version of the last Trump).

Nothing is written in stone, and individuals can make a difference. A train might look as if it’s inevitably running to a destination, but people lay the tracks. We decide the route. The lesson I’ve learned from the past few months is that denial and anger achieve nothing. The only thing that will make a difference – and make you feel better about the situation – is to vow that this will not stand. I will fight the reactionary, small-minded thinking that underpins Brexit. You must fight the manifest absurdities of Trumpism. Make America great again in your own way.

• This article was amended on 7 November 2016. A previous version said a referendum was held in 1975 to join the the forerunner of the EU; it backed the UK staying in.