Woman in the United States senate (4)
I believe the answer is:
tess
'woman' is the definition.
'in the united states senate' is the wordplay.
'in' indicates the answer is hidden within the clue.
'TESS' can be found hidden inside 'united states senate'.
(Other definitions for tess that I've seen before include "Thomas Hardy heroine" , "tragic heroine" , "Hardy's pure woman" , "Hardy's Durbeyfield heroine" , "20 heroine" .)