Forces politician into terrible lies (6)
I believe the answer is:
impels
'forces' is the definition.
('impel' can be a synonym of 'force')
'politician into terrible lies' is the wordplay.
'politician' becomes 'mp'.
'into' means one lot of letters goes inside another.
'terrible' is an anagram indicator.
'lies' is an anagram of 'iels'.
'mp' inserted within 'iels' is 'IMPELS'.
(Other definitions for impels that I've seen before include "Forces, urges to action" , "Urges forward" , "Drives on in simple way" , "Drives or forces" , "Urges or drives to do something" .)