Unilateral withdrawal could seriously damage NATO credibility

This depends on the context and circumstances: If it were to be a forced decision by the US administration, the consequences would be dramatic. If Germany were to take this decision with the consent of NATO partners it would be regrettable, but its impact would be limited if it happened within the context of a general and consensual “reshuffling” of NATO's nuclear posture (for instance, Polish sharing, etc.). If Germany decides unilaterally – without the consent of its NATO partners – it would be Berlin’s sovereign right. But it could seriously damage the political credibility of NATO's deterrence posture, especially given that it could have serious “ripple effects” (debates in the Netherlands, Belgium etc.). Finally, the argument according to which “extended deterrence can exist without sharing” is moot, since we are not starting from scratch but talking about a radical change in NATO policy.