Attacked tired Welsh politician first (8)
I believe the answer is:
ambushed
'attacked' is the definition.
(to ambush is to attack)
'tired welsh politician first' is the wordplay.
'tired' becomes 'bushed' (similar in meaning).
'welsh politician' becomes 'AM' (Assembly Member, from National Assembly of Wales).
'first' means one lot of letters go next to another.
'bushed' put after 'am' is 'AMBUSHED'.
(Other definitions for ambushed that I've seen before include "Taken by surprise in war" , "surprised?)" , "Attacked (someone) from concealment" , "Lay in wait and waylaid" , "taken, surprisingly" .)