I would not trust him to run a bath, let alone drive a car.
After seeing his indecisiveness, I would not trust him to run a bath, let alone make a decision.
Given his lack of culinary skills, I would not trust him to run a bath, let alone cook a meal.
Considering how forgetful he is, I would not trust him to run a bath, let alone watch my pet.
With his reckless spending habits, I would not trust him to run a bath, let alone handle my finances.