The overwhelmingly likely result of the next London mayoral election is that Sadiq Khan will be comfortably re-elected.

The extreme likelihood of defeat means that running against Khan is win-win for an ambitious Conservative. Lose and you have exceeded expectations. You are instantly a “big beast”, whose thoughts on crime, housing, integration and a swathe of other topics are considered worthy of consideration.

Lose while cleansing some of the taint of Zac Goldsmith’s dog-whistle campaign against Khan in 2016 – which many senior Tories believe should be their real aim in the next London election – and you have exceeded expectations and are a voice on matters relating not only to the capital but also to the future of the Conservative Party and how it wins over graduates, ethnic minorities, social liberals and other groups that cluster in the big cities.

And, of course, they just might win. It’s not very likely but you can see how, if crime continues to rise, if the Conservative candidate can blame Khan without endorsing the grim Islamophobia that has characterised some of the attacks on the Mayor’s record as far as crime goes, if they can navigate the electoral damage of Brexit, if the economy suddenly improves, if Khan makes a major misstep; you can just about see how a Conservative candidate could win in 2020. It requires a lot of good luck on their part and a lot of bad luck on Khan’s part, but it’s there.

So the prize is real and the consequences even of losing are pretty good if you are Justine Greening, James Cleverly, Munira Mirza, or anyone else who might fancy having a go at it, in most possible universes.

Because there is another possible outcome of the London mayoral race, and it goes like this: Brexit is a disaster, which hits London and annoys many traditional Conservative voters in the capital, who either stay home, vote Labour as a protest or a bit of both. Khan successfully turns the election into a referendum on Heathrow and Brexit, which hurts the Tories very badly in Richmond, Twickenham and Hillingdon, three boroughs in which the Conservative candidate must win big to have any chance of winning the mayoral election. A national scandal – like say, Windrush – which offends everyone, but London in particular, hits the Conservatives in the run-up to polling day. Khan not only wins but wins outright in the first round. The Tory candidate is no big beast, no important voice in the party’s debate, but a scapegoat. That’s the downside risk for any candidate.