Prime minister loses case for state (6)
I believe the answer is:
israel
'state' is the definition.
(Israel is an example)
'prime minister loses case' is the wordplay.
'prime minister' becomes 'disraeli' (I've seen this before).
'loses case' means to look at the middle letters (the case is the outside letters).
The central letters of 'disraeli' are 'ISRAEL'.
'for' is the link.
(Other definitions for israel that I've seen before include "Middle Eastern state" , "Eastern Med nation" , "Serial (anag)" , "Strange serial state" , "Middle-Eastern country" .)