Forward striking idiot with supporters having invaded (4,2,5)
I believe the answer is:
bold as brass
'forward' is the definition.
I don't know anything about this answer so I can't judge whether it can be defined by this definition.
'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' means one lot of letters go next to another.
'supporters' becomes 'bras' (a bra gives support to breasts).
'having invaded' indicates putting letters inside.
'bold'+'ass'='boldass'
'boldass' going 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".)