Officially, no, but it is an emergent property of their other responsibilities.

For instance, a government cannot maintain law and order without power, and a society without law and order is the definition of a failed state ([edit] well, more specifically one in which the government has lost its monopoly on violence). It's not an unreasonable interpretation to therefore say any non-failed state must retain power.

It is, sort off, the inherent goal of a (nation-)state. At least, that is a common and rather accurate historical and geopolitical model.

maybe it's not the job, but it's the nature of governments