In a democracy the three branches are independent. Democracy is not just 'you get to elect the guy on top', it also attempts to preserve the rights of the population. If the population does not have rights, democracy soon becomes very fake. E.g., I don't like this or that party so I throw anyone in jail during election day if I know that they would vote for the wrong party. The general principle is that if a person/organization has too much power they will generally find a way to abuse it. The famous split-up in three branches is employed to a greater or lesser extend in all countries where the rights of the population are respected.