Gather supporters with alcohol in Irish party (4,2)
I believe the answer is:
drum up
'gather supporters with' is the definition.
I can't judge whether this defines the answer.
'alcohol in irish party' is the wordplay.
'alcohol' becomes 'rum' (alcoholic spirit).
'in' means one lot of letters goes inside another.
'irish party' becomes 'dup' (Democratic Unionist Party).
'rum' going inside 'dup' is 'DRUM UP'.
Can you help me to learn more?
(Other definitions for drum up that I've seen before include "To attract" , "Attempt to obtain (support)" , "Bring about (something) by constant and persistent effort" , "Obtain through vigorous effort - and percussion?" , "Try to get (something) by canvassing" .)