Boris Johnson will swerve the Channel 4 debate on Sunday, as his campaign continues to minimise its exposure to scrutiny and to risk. The former foreign secretary will, however, attend the BBC’s debate on Tuesday evening, when the field will have further narrowed.

There are a variety of reasons why the former mayor’s interests are well-served by avoiding the debate: the biggest one of course is that he is currently the frontrunner and it is in the interests of the frontrunner to avoid moments that could change the contest.

There are also a number of specific threats. The biggest in the eyes of the press at this debate is Rory Stewart, who has been the most outspoken critic of Johnson personally. But bluntly, there is very little that Stewart can say about Johnson that will damage him. Johnson’s parliamentary supporters aren’t backing him because they believe he has the purest character, or the best record in office, but because they think one or all of the following: that he is the politician who can get Brexit resolved, put Nigel Farage back in his box, win the next election, or that he is going to be the next Conservative Prime Minister anyway so better to live on your knees than to die on your feet.

His coalition among the Conservative membership likewise rests on members who think he can win elections, and members who think he can be trusted on Brexit. Johnson’s biggest political assets are his victories in the mayoral elections of 2008 and 2012 and the referendum of 2016, rather than anything else.

In Parliament, he has a coalition of people who are ideologically attuned to him and people who want jobs under him. This coalition has radically different ideas about how to resolve Brexit – some are ardent supporters of no deal, others fear that a no deal Brexit would bury the party. Some want to avoid an election, others believe that it is inevitable.

So the two big threats to Johnson are a) that another candidate will be able to successfully prosecute the argument that they, not he, are the party’s best bet electorally speaking; and b) that his parliamentary coalition will break up between now and the final ballot.

By swerving this first debate, Johnson is increasing the risk of that one of Jeremy Hunt, Michael Gove, Dominic Raab or Rory Stewart might sufficiently wow the nationally-representative studio audience to up-end the contest. But the price of increasing risk a) is that he is decreasing the chances of risk b).

Why? Because the candidate who Johnson will be most well served by the absence of now and that BBC debate isn’t Rory Stewart – it’s Dominic Raab, the only other impeccable No Deal advocate left in the contest. If Raab is eliminated between now and then, Johnson’s parliamentary balancing act gets a lot easier. He will be the most extreme pole of the Conservatives’ Brexit debate and that will make it easier for him to avoid being pinned down by anyone.

The difficulty for Johnson is that it is not guaranteed that Raab will be eliminated. While some of Raab’s supporters are privately considering throwing in the towel, supporters of the already-eliminated Andrea Leadsom and Esther McVey are both contemplating that they are better served by backing Raab than Johnson, for multiple reasons. Some ambitious MPs think it is too late to secure preferment under Johnson, but that an empowered Raab might be a useful advocate for “his” people later down the line. Other, more suspicious parliamentarians, don’t want advocates of no deal to be confined to a menu that consists solely of Johnson.

And the challenge of navigating that field is a lot bigger than fielding some harsh words from Rory Stewart.