Take steps with fellow politician to secure agreement (7)
I believe the answer is:
compact
'agreement' is the definition.
(compact is a kind of agreement)
'take steps with fellow politician' is the wordplay.
'take steps' becomes 'act' (synonyms).
'with' means one lot of letters go next to another.
'fellow' becomes 'co' (I've seen this in other clues).
'politician' becomes 'mp' (Member of Parliament).
'co'+'mp'='comp'
'act' put after 'comp' is 'COMPACT'.
'to secure' acts as a link.
(Other definitions for compact that I've seen before include "Close - agreement - make-up case" , "An official agreement" , "Small and neat - agreement" , "The powder-box is closely packed" , "What comes initially with CD" .)