Ulterior motive - as a solver might discern in stag (endangered) (6,6)
I believe the answer is:
hidden agenda
'ulterior motive' is the definition.
(I've seen this before)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for hidden agenda that I've seen before include "Sub-text, unstated objective" , "followed in secret meeting?" , "Concealed intentions" , "that could delay the meeting?" , "covert plan" .)