Two Republicans hugging are less common (5)
I believe the answer is:
rarer
'less common' is the definition.
('rare' can be the opposite of 'common' so perhaps 'rarer' is reasonable for 'less common')
'two republicans hugging are' is the wordplay.
'two republicans' can mean two replacements for 'republican'.
'republican' becomes 'R' (political abbreviation).
'republican' becomes 'R' (political abbreviation).
'hugging' indicates putting letters inside (outside letters hug or embrace inside letters).
'r'+'r'='rr'
'rr' placed around 'are' is 'RARER'.
(Other definitions for rarer that I've seen before include "More scarce or uncommon" , "More unusual" , "Thinner" , "even less common" , "Stranger" .)