Forward striking idiot with supporters having invaded (4,2,5)
I believe the answer is:
bold as brass
'forward' is the definition.
I know nothing about this answer so I cannot judge whether this works.
'striking idiot with supporters having invaded' is the wordplay.
'striking' becomes 'bold' (I've seen this in another clue).
'idiot' becomes 'ass' (both can mean a stupid person).
'with' says to put letters next to each other.
'supporters' becomes 'bras' (a bra gives support to breasts).
'having invaded' means one lot of letters goes inside another.
'bold'+'ass'='boldass'
'boldass' placed around 'bras' is 'BOLD AS BRASS'.
Can you help me to learn more?
(Another definition for bold as brass that I've seen is " Utterly unabashed".)