Of all the time-honored failings for which we criticize sitting presidents — by “we” I mean pundits, academics and other members of the chattering phylum — two charges stand out: imperialism and shrinkage. Usually it’s one or the other. When the president is unpopular or when he’s lost control of his agenda or when he just seems inadequate to the demands of the job, the headline “The Incredible Shrinking Presidency” proliferates like kudzu.