Assume control (4,4)
I believe the answer is:
take over
'assume control' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for take over that I've seen before include "Assume control of" , "Act of assuming control" , "This bid is for control of a business" , "Company buyout" , "Buying out of one company by another" .)