Stimulate early leftist to maintain steady progress (7)
I believe the answer is:
jogtrot
'maintain steady progress' is the definition.
(horse-riding term)
'stimulate early leftist' is the wordplay.
'stimulate' becomes 'jog' (jogging is a kind of stimulating).
'early leftist' becomes 'trot' (short for Trotskyist).
'jog'+'trot'='JOGTROT'
'to' is the link.
(Other definitions for jogtrot that I've seen before include "boring routine" , "exercise" .)