Reason fever overwhelms resistance (5)
I believe the answer is:
argue
'reason' is the definition.
(I know that reason can be written as argue)
'fever overwhelms resistance' is the wordplay.
'fever' becomes 'ague' (I've seen this before).
'overwhelms' indicates putting letters inside.
'resistance' becomes 'r' (electronics abbreviation).
'ague' going around 'r' is 'ARGUE'.
(Other definitions for argue that I've seen before include "Dispute - debate" , "Dispute, bicker" , "Discuss, contend" , "Have a difference of opinion" , "Heatedly exchange views" .)