Tried mightily (6)
I believe the answer is:
strove
'tried mightily' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for strove that I've seen before include "Voters (anag) - made every effort" , "Made great efforts" , "Endeavoured" , "Struggled" , "Tried hard for voters" .)