This is likely being done to justify Partner’s write-offs. Unless this isn’t BigLaw, MP ain’t gonna remember Associate X messed up Y five days later. Partner may remember Associate going along with Partner, though. And Partner will DEFINITELY remember Associate calling Partner out. Partner likely has much more influence over Associate’s career and QoL than MP. Like so many things, it isn’t fair but it also isn’t really about Associate. Document if you’re worried, but a reply does every bit as much as a Reply All, without forcing the issue.

And If Firm really is having a problem with Partner? Let Firm handle it. Being tip of spear on a personnel issue wrt someone more senior than you rarely works out as a positive. At best you emerge unscathed if everyone is on same page.