Campaign lacks its ultimate material (6)
I believe the answer is:
canvas
'material' is the definition.
(canvas is a kind of material)
'campaign lacks' is the wordplay.
'campaign' becomes 'canvass' (I've seen this before).
'lacks' means to remove the last letter (I've seen 'lacking' mean this (the word is incomplete or lacking)).
'canvass' with its final letter removed is 'CANVAS'.
'its ultimate' acts as a link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for canvas that I've seen before include "Floor of a boxing ring" , "End of a racing boat; coarse cloth" , "Sail material" , "Tent material" , "Sailcloth" .)