Bulletin about split in Foggy Bottom (5,10)
I believe the answer is:
state department
'foggy bottom' is the definition.
(I've seen this in another clue)
'bulletin about split' is the wordplay.
'bulletin' becomes 'statement' (a bulletin is a statement or report).
'about' indicates putting letters inside.
'split' becomes 'depart' (both can mean to leave).
'statement' enclosing 'depart' is 'STATE DEPARTMENT'.
'in' acts as a link.
(Other definitions for state department that I've seen before include "US Foreign Office" , "American diplomats" , "Washington office" , "government agency abroad" , "US officials" .)