Right about America’s corrosive influence (4)
I believe the answer is:
rust
'corrosive influence' is the definition.
'right about america's' is the wordplay.
'right' becomes 'rt'.
'about' indicates putting letters inside.
'america's' becomes 'us' ('US' can be a synonym of 'america').
'rt' enclosing 'us' is 'RUST'.
(Other definitions for rust that I've seen before include "Reddish-brown coating formed on metal by damp" , "Reddish-brown coating formed on metal by moisture" , "Oxidisation" , "Fungal plant disease" , "Oxidised iron" .)