As the election campaign enters its third week, the Conservatives are enjoying a 17-point lead, according to a YouGov poll. However cautious Tory MPs are quick to point out nothing should be taken for granted, as this is broadly speaking where the Tory party was at this point in the 2017 campaign. But for Labour to have a chance of forming a government come 12 December, Jeremy Corbyn needs to change the political weather. He has two set piece opportunities this week to do just that: Tuesday’s leader’s debate and Labour’s manifesto launch.

ITV’s planned television debate has the potential to move the dial. The first head-to-head debate of the campaign has led to cries of foul play from smaller opposition parties who have been excluded from the meet. The Liberal Democrats have taken legal action over the exclusion of their party leader Jo Swinson from the debate.

Both main parties believe that the arrangement ought to benefit them. During the 2017 snap election, Corbyn’s popularity climbed in the wake of multiple media appearances. In contrast, risk averse Theresa May’s decision to decline an invitation to take part in TV debates (on the grounds that she preferred ‘to get out and about and meet voters’) backfired. It went on to play into a narrative of a Prime Minister avoiding scrutiny and taking voters for granted. Johnson’s team are determined not to repeat the mistakes of 2017.

The majority view in CCHQ is that a head-to-head debate ought to play to Johnson’s strengths. Unlike Theresa May, Johnson is a confident and charismatic public speaker. The hope of a head-to-head debate is that this will cement this image further with voters. If the Tories can press the message that only two candidates can be prime minister on 13 December – Johnson and Corbyn – this should boost Johnson. The question of who do you want to be PM, helps the Tories with both Tory/ Lib Dem and Tory/ Brexit party waverers.

But with Johnson already the frontrunner, the opportunity for Jeremy Corbyn is the greatest. The Conservatives’ electoral strategy rests on the party uniting the Leave vote – and the Remain vote splitting between Labour and the Lib Dems. By cutting Lib Dems out of the picture, Corbyn has a perfect opportunity to pitch himself as the only viable alternative to Johnson and the only viable route to a second referendum.

If support for the Lib Dems falls away and goes to Labour, the electoral landscape starts to look very different – and much trickier for the Tories. As former Labour pollster James Morris told the Coffee House Shots podcast last week:

‘The Labour party is not picking enough of the Remain vote up. That vote is splitting and if that vote splits, the Conservatives are going to get a majority. So if I were sitting in Labour HQ I would be thinking about what are the things we need to do to tell remain voters that we are your choice not the other people’. The debate offers a way to do this: ‘The two-head debate is that opportunity to land that message’.

Given that Corbyn repeatedly refused to say whether he would campaign for Leave or Remain in a second referendum, there’s reason to suspect he won’t go full Remain. But if Corbyn can convince Remain voters he is their best and only hope of remaining in the EU, the Tory path to a majority could look in doubt.