Staunch supporter? (4)
I believe this clue is a double definition.
'staunch' is the first definition.
(I know that staunch can be written as stem)
'supporter' is the second definition.
(I've seen this before)
(Other definitions for stem that I've seen before include "Slender upright part of wine glass" , "Staunch - stalk" , "Check - part of a plant" , "Halt flow" , "branch of family" .)
'staunch supporter' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for stalwart that I've seen before include "Sturdy, tenacious and tough" , "Steadfast" , "Loyal, reliable and hardworking" , "Tart laws could be strong and sturdy" , "Valiant" .)