Easy election victory but everything going downhill? (9)
I believe the answer is:
landslide
This clue is a double definition.
'easy election victory' is the first definition.
'everything going downhill?' is the second definition.
'but' is the link.
(Other definitions for landslide that I've seen before include "Overwhelming election majority" , "easy victory" , "Overwhelming election win" , "great electoral success" , "Large earth movement" .)