American politician contributing to tense NATO row (7)
I believe the answer is:
senator
'american politician' is the definition.
(I've seen this before)
'contributing to tense nato row' is the wordplay.
'contributing to' indicates the answer is hidden within the clue.
'SENATOR' is hidden within 'tense nato row'.
(Other definitions for senator that I've seen before include "US legislator" , "Clinton, perhaps" , "politician going wrong" , "Member of Upper House engaged in treason" , "Member of a governing body" .)