Uncertainty of opinion about US policies principally (8)
I believe the answer is:
suspense
'uncertainty' is the definition.
(I know that suspense is a type of uncertainty)
'opinion about us policies principally' is the wordplay.
'opinion' becomes 'sense' (I am not sure about this - if you are sure you should believe this answer much more).
'about' indicates putting letters inside.
'principally' says to take the initial letters.
The initial letter of 'policies' is 'p'.
'us'+'p'='usp'
'sense' going around 'usp' is 'SUSPENSE'.
'of' acts as a link.
Can you help me to learn more?
(Other definitions for suspense that I've seen before include "expectancy" , "feature of exciting fiction?" , "State of anxious uncertainty while waiting (8)" , "Apprehension, anticipation" , "State of nervous uncertainly" .)