Feeling like my authority is compromised - how to change this?

If they're actively going against you, you could try leaning on your team more - if they go against your team by going after you, the team will start to dislike Mr.TakeYourJob and may actively work against him. He may be good at brown-nosing, but if the team team hates him he won't be very effective. If this guy is going after your job, it's fair game to sabotage him when you can - especially since he did so while you were sick/absent.

In the meantime, I'd suggest looking elsewhere. 3 years solid experience that you should be able to take elsewhere. If your boss is intent on replacing you due to personality conflict, you probably don't have much of a fighting chance against Mr.TakeYourJob unless he shows himself to be incompetent. Even then, it may not be enough. Incompetent people work their way up to management all of the time.

/r/jobs Thread