A way to secure principal campaign fund (3,5)
I believe the answer is:
war chest
'campaign fund' is the definition.
(I've seen this in another clue)
'a way to secure principal' is the wordplay.
'a way' becomes 'w' (Compass direction - West).
'to secure principal' becomes 'archest' (I can't justify this - if you can you should give a lot more credence to this answer).
'w'+'archest'='WAR-CHEST'
Can you help me to learn more?
(Other definitions for war chest that I've seen before include "Funds for a campaign" , "Fighting fund" , "hypothecated funds" , "Funds set aside" , "ready for fighting?" .)