I don't think there's much doubt Starmer's credibility with the man on the street has taken a hit
I think his credibility with the man, and woman, on the street has taken a hit sometime ago, and with quite a diverse range of sections of the population.
He's a terrible Leader, largely because he tries to follow rather than lead, but lacks the political astuteness to read the country and instead listens to the loudest lobby groups. And that's why his credibility was in tatters way before this.
Unfortunately, many of his named contenders are not any better. So it may be from the frying pan to the fire for the country.