1. Brexit is clearer and harder than in 2017. Tories have swung towards the harder end of the Brexit spectrum and are actively flirting with no deal.
2. A long-standing MP is quitting.
4. The Brexit Party may well stand and strip off some of the Leave vote.
All these changes suggest they should be much more "winnable" than if their MPs had toughed it out another cycle.
But if they stand down it's a clean slate, and voters will evaluate each candidate afresh.