Until recently, the prospect of Theresa May flopping in this general election would have been absurd - but today’s YouGov poll shows her lead cut to just five points, less than a quarter of its peak. Converted into seats, that would mean a majority of just two MPs, down from the 17-strong majority achieved by David Cameron against Ed Miliband. At a time when the extraordinary is happening all the time, it is impossible to dismiss this opinion poll.

The public like her style, but her shambolic U-turn over the so-called ‘dementia tax’ has given everyone cause to doubt whether she is as ‘strong and stable’ as she says she is. In fact, she can look indecisive and a bit dozy. She repeatedly promised us that she would not hold a general election, but then did. She made National Insurance increases the cornerstone of her first Budget, only to abandon the idea days later when she worked out that it violated her manifesto pledge. And she made the abolition of the cap on care home fees the single most significant announcement of her manifesto launch, then abandoned that as well when working out that critics would lampoon it as a 'dementia tax'. The Andrew Neil interview – and the BBC News at Ten on Monday night - showed the way that her campaign was going. Politics was suspended by what happened at 10:33pm that night but, as Philip Collins says in the Times today, people have not forgotten about the debacle.

In this ridiculously personalised campaign – she always asks us to vote for ‘me and my team’, rather than her party – the personal credibility of the leader matters more than ever. And if the leader is in the habit of accidentally firing tornadoes at her own credibility, then this matters too.

Not since Labour's 1983 'Suicide note' has a manifesto launch done so much to cheer the other side. I'm not sure quite what the thinking was behind those fervent disavowals of right-wing politics and the embrace of bad Labour ideas, but if the aim was to lure Labour voters then it doesn't seem to have been a great success. The Labour recovery - Corbyn surge, even - is nothing short of extraordinary.

The Tory lead has already fallen from 22 points to 5 points and if there is a another debacle on the scale of the ‘dementia tax’ there might be no majority at all. I actually agreed with Nick Timothy’s policy on care for the elderly: I praised it as a 'bold and necessary' move in my Daily Telegraph column, and still think that his basic point – those who can afford to pay should pay – is not just the best answer but the only answer to the conundrum of social care. And I virulently disagreed with my colleague Will Heaven who christened it as a 'dementia tax' here on Coffee House. We recorded our disagreement in a podcast here:

Will Heaven and Fraser Nelson debate the 'dementia tax':

But if the PM was not willing to defend Nick Timothy's policy, she should never have launched it – or, indeed, gone near such a combustible topic. A policy idea like this needs robust, clear and repeated explanation – not a paragraph dropped at late notice in the manifesto that even Cabinet members don’t understand. To drop the idea on the grounds that Jeremy Corbyn was being rude about it was a sign of weakness.

Of course, Theresa May claims she never intended to abolish the cap on social care costs. If true (a big 'if') then this is a staggering communications failure. Why allow her Health Secretary to go on the radio saying that the cap was being abolished? Couldn't even he be briefed correctly? And if he misspoke, then why not correct the record immediately? Never has the PM looked weaker than she did when trying this implausible excuse out on Andrew Neil.

In my view, the U-turn was far worse than the policy. The policy was a tough sell, but it was sellable. Yet it seems the Tory party – sorry, Theresa May’s team – was not prepared to sell the argument, because it had no prior knowledge of the argument. Because that's how she rolls.

This is easily remediable: if she cannot see around corners, she should employ people who can. And communication: she needs to find good people, trust them and take their advice. In this case, she needed someone to say: Nick’s right, this care idea is a brave policy. But to launch a big new idea in the middle of a general election campaign is dangerous. And given time constraints, our lack of message testing and the overall unpreparedness of the ministers who would be defending this idea, it’s not the right time. So: yes to the policy, no to a campaign-time launch.

My gut feeling is that the next YouGov poll will show a stronger Tory lead as the nation considers security, and Jeremy Corbyn’s inability to provide that security: it's his turn to meet Andrew Neil tonight. So let's see what that interview, and the weekend polls, bring.