the weak link (in the chain)
idiomPart ofchain
the weak link (in the chain) — idiom
1. The part of a system or group that is most likely to fail or cause problems.
1.idiom
Definition
The part of a system or group that is most likely to fail or cause problems.
Example
Brian's poor communication skills were the weak link in the team.
Is the old server the weak link in your network security?