Holding that temporal proximity of "a few months" between a protected activity and an adverse employment action "suffices to establish a minimal prima facie case of retaliation, [but] it does nothing to refute the government's proffered legitimate reasons for disciplining [the plaintiff]"
Holding that, in balancing the scope of reasonable opposition conduct, "[t]he requirements of the job and the tolerable limits of conduct in a particular setting must be explored"