Gloomy Republican trapped by American elk (6)
I believe the answer is:
morose
'gloomy' is the definition.
(I've seen this in another clue)
'republican trapped by american elk' is the wordplay.
'republican' becomes 'R' (abbreviation in US politics).
'trapped by' indicates putting letters inside.
'american elk' becomes 'moose' (I've seen this before).
'r' inserted into 'moose' is 'MOROSE'.
(Other definitions for morose that I've seen before include "dark" , "grouchy" , "Gloomy and unsociable" , "Silent, gloomy and ill-tempered" , "in gloomy mood" .)