One-Eyed Watchdog

Someone who presents as concerned about an issue (antisemitism, free speech, death threats, political violence, lack of scientific rigor in some study, etc.) but only speaks up when political opponents commit the transgression, while guilty allies are ignored or defended.

Synonym - Hypocrite

Karen was outraged when Kavanaugh was accused but turned into a One-Eyed Watchdog when Biden and Cuomo were accused.