Reason I vote differently after Macron's summit (6)
I believe the answer is:
motive
'reason' is the definition.
(I know that motive is a type of reason)
'i vote differently after macron's summit' is the wordplay.
'differently' is an anagram indicator.
'after' means one lot of letters go next to another.
'summit' indicates taking the first letters (the letter at the top is the summit).
The first letter of 'macron' is 'm'.
'i'+'vote'='ivote'
'ivote' anagrammed gives 'otive'.
'otive' after 'm' is 'MOTIVE'.
(Other definitions for motive that I've seen before include "Underlying purpose" , "Purpose - reason" , "Reason behind an action" , "Reason for doing something, perhaps a crime" , "Underlying intention" .)