Employee undermining you
Find out if others are being sabotaged as well. Save emails and communications with the underminer. Keep notes on undercutting behaviors with details of occurrences. Nurture the relationship with your boss, as much as it makes sense (perhaps no need for brown nosing). Do favors for the more ones you have under your belt, the less someone can truly undermine you. If the underminer is hiding things from you, which is very likely, your network of colleagues is invaluable. Approach him assertively, when he does something specific against you.