One legislator has every other urgent challenge (6)
I believe the answer is:
impugn
'challenge' is the definition.
(impugning is a kind of challenging)
'one legislator has every other urgent' is the wordplay.
'one' becomes 'I' (Roman numeral).
'legislator' becomes 'MP' (an MP legislates in parliament).
'has' is a charade indicator (letters next to each other).
'every other' indicates alternate letters.
The alternate letters of 'urgent' are 'ugn'.
'i'+'mp'+'ugn'='IMPUGN'
(Other definitions for impugn that I've seen before include "Dispute the truth of" , "Call into question or attack by words" , "Attack as false, challenge" , "Try to discredit, express doubts about honesty" , "Nip mug badly and call in question" .)