Force politician into fabrication of lie (5)
I believe the answer is:
impel
'force' is the definition.
('impel' can be a synonym of 'force')
'politician into fabrication of lie' is the wordplay.
'politician' becomes 'mp'.
'into' means one lot of letters goes inside another.
'fabrication of' indicates anagramming the letters (I've seen 'fabrication' mean this).
'lie' with letters rearranged gives 'iel'.
'mp' put inside 'iel' is 'IMPEL'.
(Other definitions for impel that I've seen before include "Motivate" , "Make" , "'Drive, force (5)'" , "Force into motion" , "Egg" .)