### Clue: Turn on US president (wife getting chop) (9)
### Answer: BUSHWHACK 
 ### Explanation: Definition: Turn on
 BUSH(George H.W. or his son, George W., US presidents) + W(abbrev. for "wife") **plus**(getting) HACK(to chop/to cut with heavy blows).
Defn: In the US, to launch a surprise attack on someone.