James Frayne is Director of Public First and author of Meet the People, a guide to moving public opinion.

Should the Conservatives go negative on Corbyn at the next election? After all, a reasonable argument goes, the party went hard against Corbyn last time and it made no difference; arguably, it was even counter-productive. Why would it be different now? In my view, they’d be mad not to make him a defining feature of their campaign. There are five reasons why.

Firstly, and most importantly, Corbyn’s reputation is in a totally different place to 2017. While it’s true his initial ratings were poor and then surged during the campaign in 2017, it’s highly unlikely the same would happen again. Then, he was essentially an unknown entity and he was introduced to the public amid combat with a desperately poor Conservative candidate. He quickly emerged as a plucky fighter against the apparently unstoppable May-led Conservative Government.

In 2019, people know much more about him and they dislike what they see. Even left-leaning voters have tired of him – believing he can’t hold the Government to account. The party needs to remind people they’re choosing between specific prime ministerial candidates and specific potential governments. In doing so, there’s less of a risk of creating a unifying force around Corbyn. That doesn’t mean trying to turn the election into a quasi-presidential race – as Boris Johnson is hardly a unifying candidate – but it does mean that the party should be running a contrast campaign with ‘Corbyn’s Labour’.

Secondly, relatedly, he’s incredibly unpopular with working class swing voters. I’m not entirely sure why, but around a year ago Corbyn’s ratings went off a cliff. They’d been sliding slowly but surely since 2017, but something really changed a year ago. Perhaps it was related to antisemitism, perhaps also to exasperation with the lack of progress on Brexit. As I wrote last time, I’m nervous the Conservatives haven’t done enough to secure the votes of the Midlands and Northern working class (and I’m more nervous having spent much of the week in inner-city Nottingham and Derby). But with Corbyn leading the Labour Party – and the Conservatives making him the only face of the party – they stand a much better chance of converting these voters.

Thirdly, the party must ensure he plays the role of a useful prop in their anti-establishment / anti-politics campaign. Last time around, the Conservatives failed to portray the new PM as a change candidate and they paid a heavy price. The public still want change. While the Conservatives can demonstrate change through issues to a degree (tougher crime policies etc), they also need to use the relative character strengths of Boris Johnson against Jeremy Corbyn. In short, people think Boris Johnson is a different sort of politician – someone who’s prepared to smash the system up to deliver change. (Time will tell how much slack the public will cut him for his missed deadline; I think a little).

On the other hand, increasingly Corbyn is looking like ‘just another politician’ who talks in riddles, who doesn’t stand for anything and who you can’t trust. As such, the Conservatives need to endlessly contrast what amounts to ‘change versus more of the same’. This amounts to a total reversal on 2017 when Corbyn was the anti-politics candidate.

Fourthly, Corbyn is one of the only Labour politicians the public knows, other than Diane Abbott. A very small number of people know about John McDonnell, but the rest are unknown. The Conservatives have to focus on Corbyn just to secure traction. There’s no way they can start introducing new politicians to the public at this late stage. Furthermore, the fact remains that Labour’s reputation generally far, far outperforms that of Corbyn. It would make no sense to focus on the Labour Party when the public – including working class swing voters – hold Labour in ultimately pretty high regard.

Fifthly, and finally, the Labour Party will surely be trying to diversify their spokespeople in the next campaign. They’re not stupid; they know they need to promote other voices when Corbyn’s ratings are so poor. In doing so, in using the likes of Angela Rayner and even John McDonnell (who performs well in the media even if his views, were they known, would make many voters queasy) they’re likely to perform better. In turn, the Conservatives will need to stop them doing this and to ensure the public keep picturing Corbyn’s face when they think of Labour.

In short, while there’s a case both that the Conservatives just run a campaign focused entirely on issues (‘get Brexit done with us’) or that they sign some positive campaigning pledge, these are outweighed by the need to make this election all about Corbyn.