It wasn’t a mistake, it was series of deliberate moves culminating in the ‘Kamikaze Budget’.
1st the sacking of Sir Tom Scholar permanent secretary at the Treasury, to clear the decks for the idiocy to come.
2nd The refusal to accept a OBR impact analysis and lie about it not being available.
3rd The absence of a fiscal plan and then lying about it being available.
4th Announcing massive un costed tax cuts non of which were at all necessary that overwhelmingly benefitted the already wealthy and lying about it.
Non of this was a mistake, they were the actions of an idiot ideologue drunk on power.
The polls disagree with you on Labour.