FBI agent backed objective to protect (6)
I believe the answer is:
defend
'protect' is the definition.
(I've seen this before)
'fbi agent backed objective' is the wordplay.
'fbi agent' becomes 'fed'.
'backed' says the letters should be written backwards.
'objective' becomes 'end' (I've seen this before).
'fed' backwards is 'def'.
'def'+'end'='DEFEND'
'to' is the link.
(Other definitions for defend that I've seen before include "Stand up for" , "Block, as in cricket" , "Protect or assist against attack" , "Safeguard" , "Resist an attack" .)