After the experience of the last couple of years, surely only a mug would offer a rash prediction about the outcome of the general election – as Prime Minister Ed Miliband, President Hillary Clinton and the winning remain campaign can testify. But here’s one all the same: whether she wins or loses, and even if she bags a much enhanced majority, Theresa May will not fight another general election.

That’s chiefly because, as a candidate, she’s proven herself to be jaw-droppingly bad. When she called this election, on April 18, May had a poll lead so large it may always have been illusory. But then she seemed to set out, methodically and with great purpose, to reduce it.

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The first move was to make the centrepiece of her manifesto a proposal to force the elderly to pay for their social care out of the value of their house, taking all but their last £100,000. Had you sat in a laboratory designing a policy intended to lose the Tory party votes, you’d have struggled to do better. The Labour peer Maurice Glasman likes to joke that just as Field Marshal Montgomery insisted that the first rule of warfare is “Never invade Russia”, so the first rule of British politics is: “Never touch people’s houses.” They rarely like it.

The dementia tax, hitting a core Tory constituency – the homeowning elderly – was self-harming enough. That May did it without preparing the ground – setting out the problem, being seen to consult widely, ensuring her cabinet colleagues were all on side – made it worse. But there was more to come.

The eventual and inevitable U-turn obviously involved a loss of face. But May compounded it by denying that she’d done any such thing. “Nothing has changed,” she said to an incredulous press corps and public. She was exposed as a fool – and, worse, someone who took voters for fools.

She could have survived the dementia tax debacle, even making a virtue of her climbdown. “It shows I listen,” she might have said. (Interestingly, some focus groups have picked up admiration for May on this ground, despite herself.) But that would have required some suppleness as a media performer. And on this score, too, she has been woeful.

May ducked face-to-face debates with her Labour opponent. True, incumbent prime ministers do that, David Cameron included. But May went further, seeking to avoid media scrutiny altogether. She said no to the Today programme (as did, to be fair, Jeremy Corbyn), said no to Channel 4 News, and said no to Woman’s Hour – instead sending Amber Rudd, days after the death of Rudd’s father. May looked, to deploy Margaret Thatcher’s favourite bit of Lincolnshire dialect, frit.

And when she did appear on TV … oh, dear me. She revealed herself to be stilted, faltering and seemingly unable to answer any question put to her. Nervous, she has an unfortunate grimace reflex that is aggravated under pressure. Even when confronted by a nurse whose pay has been stagnant since 2009, she was unable to make a human connection, instead delivering a lecture about “the magic money tree”.

The benign reading is that May is congenitally shy, and campaigning is painful for her. The harsher view is that she lacks courage, and is fearful of saying anything that might involve even the most modest risk. Note the quickfire interview where she was asked whether she preferred Sherlock or Midsomer Murders, only to answer: “I’ve watched both.” (Whisky or wine? “Depends on the circumstances.”) Asked recently what was the naughtiest thing she’d ever done as a child, her answer involved running through fields of wheat – and was agonising to watch.

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There was a solution available to May. She could have said: “It’s true, I’m a terrible campaigner. If you want the leader of a protest movement, vote for Jeremy Corbyn. But if you want a prime minister, vote for me.” It would have turned her opponent’s strength into a weakness, and her weakness into a strength. The trouble is, such a move would have required the very communications skills she lacks.

The result is that if Theresa May wins this election, it will be despite the campaign she has just fought, not because of it. On a human level, she would be forgiven for wanting never to put herself through such an ordeal again. On a less human level, the Tory party are ruthless in their will to power. Even if they get a big majority on Thursday, they will not forget the campaign they have witnessed. Barring an earthquake in the coming years, they will ensure May does not get a chance to repeat it.