In The Conservatarian Manifesto — which I finished last night and, as The Daily Shot might put it, heartily recommend — Charles C. W. Cooke writes:

By custom, we allow politicians to retain their titles for life. Throughout the 2012 election, Mitt Romney was referred to as “Governor Romney,” when in fact he had not been in public office for six years. One can only ask, “Why?” America being a nation of laws and not men, political power is not held in perpetuity, and there is supposed to be no permanent political class. Americans do not have rulers, they have employees— men and women who can be hired and fired at will and who remain subordinate both to the highest law in the land and to the popular will that it reifies. It is wholly proper for individuals to adopt titles when they have been hired by the people. But it is utterly preposterous for those individuals to retain those titles when their commission has come to an end. To my leveling tastes, even titles such as “Doctor” and “Professor” should be limited to the workplace. But at least those honorifics denote a permanent achievement or skill set. “Governor” is, by definition, a temporary responsibility. A citizen maintaining it after he has left office makes about as much sense as a retired CEO insisting that he be referred to as “Chief Executive” after he has left his post.