Merciful Russian leader embracing European traditions, initially (7)
I believe the answer is:
lenient
'merciful' is the definition.
('lenient' can be a synonym of 'merciful')
'russian leader embracing european traditions initially' is the wordplay.
'russian leader' becomes 'lenin' (I've seen this before**).
'embracing' indicates putting letters inside.
'european' becomes 'e' (abbreviation e.g. EU).
'initially' says to take the initial letters.
The initial letter of 'traditions' is 't'.
'lenin' enclosing 'e' is 'lenien'.
'lenien'+'t'='LENIENT'
(Other definitions for lenient that I've seen before include "Mild and tolerant" , "Forgiving, gentle" , "'Indulgent, easy (7)'" , "Forgiving, soft" , "Clement" .)