Supported DUP, the old leaders having deserted (6)
I believe the answer is:
upheld
'supported' is the definition.
(upholding is a kind of supporting)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for upheld that I've seen before include "Sustained" , "Maintained (decision)" , "Confirmed something disputed" , "Maintained (a custom)" , "Supported decision or belief" .)