Democrat winning legal round before US two-timing (11)
I believe the answer is:
duplicitous
'two-timing' is the definition.
(two-timing means duplicitous or deceitful)
'democrat winning legal round before us' is the wordplay.
'democrat' becomes 'd'.
'winning' indicates putting letters inside (some letters win or obtain others).
'legal' becomes 'licit' (similar in meaning).
'round before' becomes 'upo' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'licit' inserted inside 'upo' is 'uplicito'.
'd'+'uplicito'+'us'='DUPLICITOUS'
(Other definitions for duplicitous that I've seen before include "Deceitful, double- dealing" , "Double-dealing" .)