Just to add to Markproxy's answer:
"Go over his head" is a common idiom in English meaning to bypass a person in authority and seek approval from that person's boss. Like if you asked your immediate supervisor for permission to take a vacation, and he said no, and so you want to the department manager (assuming the "department manager" is the "supervisor"s boss) and asked him to overrule the supervisor and give you permission, that would be "going over the supervisor's head".
So going "over the heads of democratic leaders" would be trying to do something that the democratic leaders had rejected by appealing to some higher or more powerful authority. I'd have to read the context to see what that authority is, whether it means international bodies or military force or what.