Campaign ad covers front of office in maroon (7)
I believe the answer is:
crusade
'campaign' is the definition.
(I know that Crusade is a type of expedition)
'ad covers front of office in maroon' is the wordplay.
I cannot quite see how this works, but
'ad' is present in the answer.
The remaining letters 'cruse' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for crusade that I've seen before include "Drive" , "Used car involved in campaign for a cause" , "Advertising campaign" , "Holy war" , "Religious war" .)