Men probing underlying cause of fallen cradle? Dodgy old seat (6,7)
I believe the answer is:
rotten borough
'dodgy old seat' is the definition.
(historical term for a dodgy parliamentary seat)
'men probing underlying cause of fallen cradle?' is the wordplay.
I cannot quite understand how this works, but
'men' could be 'or' (military abbreviation for Other Ranks) and 'or' is located in the answer.
'of' could be 'o' and 'o' is present in the answer.
This explanation may well be incorrect...
(Other definitions for rotten borough that I've seen before include "old constituency" , "English parliamentary constituency of a kind abolished by the 1832 Reform Act" , "Tiny-electorate seat (hist.)" , "Corrupt constituency in former times" .)