Politically, the West Coast usually erupted, we’re told (4)
I believe the answer is:
blue
'politically the west coast usually' is the definition.
(the US west coast typically votes Democrat ie blue)
'erupted we're told' is the wordplay.
'erupted' becomes 'blew'.
'we're told' indicates a 'sounds like' (homophone) clue.
'blew' sounds like 'BLUE'.
(Other definitions for blue that I've seen before include "Oxbridge player" , "Colour - smutty" , "over-extravagant" , "It's used to whiten laundry" , "Sad; university sportsman" .)