What's up with politician getting illegal substance? (4)
I believe the answer is:
hemp
'illegal substance?' is the definition.
(cannabis)
'what's up with politician' is the wordplay.
'what' becomes 'eh' (sound used to ask 'what?' or 'pardon?').
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'with' means one lot of letters go next to another.
'politician' becomes 'MP' (Member of Parliament).
'eh' back-to-front is 'he'.
'he'+'mp'='HEMP'
'getting' is the link.
(Other definitions for hemp that I've seen before include "Plant fibre used to make rope" , "Grass" , "Narcotic drug" , "Cannabis sativa" , "Plant for rope or pot" .)