What about the first-time incumbency effect?
The betting chart above on which party will win most seats at the next general election reflects the political history of the last 6 months. Most of the time until the early summer Boris Johnson looked as though he could lead the party to another victory.
Then we had the difficult revelations about what happened at Number 10 Downing Street during the strict lockdowns. Johnson received a fine and so did Sunak something that has not been highlighted much. Things started to move, Johnson went, and the early betting market reaction to Liz truss was positive returning the Tories to the favorite slot for a week or so.
Then of course we had the disastrous call Kwartang budget and the appalling reaction to it. The Chancellor resigned and so did Truss herself a short time later. Since then the huge LAB leads in the opinion polls have driven the betting although I now think that LAB might be overstated and the Tories understated.
A really telling thing is that Sunak received no new leader bounce.
One aspect that we have not discussed has been the first-time incumbents effect. This could help MPs who first won their seats at the 2019 general election. There is evidence that MPs in such a situation can receive a boost in their first election defence. The only problem here is the new boundaries can reduce the link between the defending MP and constituents.