Campaign of intimidation was forever struggling to encompass the end of Putin (3,2,6)
I believe the answer is:
war of nerves
'campaign of intimidation' is the definition.
'was forever struggling to encompass the end of putin' is the wordplay.
'struggling' is an anagram indicator.
'to encompass' is an insertion indicator (I've seen this in other clues).
'the end of' indicates one should take the final letters.
The final letter of 'putin' is 'n'.
'was'+'forever'='wasforever'
'wasforever' is an anagram of 'waroferves'.
'waroferves' going around 'n' is 'WAR OF NERVES'.
(Other definitions for war of nerves that I've seen before include "Psychological tactics in contest" , "Psychological conflict" .)