So maybe Chief Justice Roberts was instinctively editing and "improving" the wording of the constitutional oath.

Steven Pinker has the theory:

How could a famous stickler for grammar have bungled that 35-word passage...? ... [A simple] explanation is that the wayward adverb in the passage is blowback from Chief Justice Roberts’s habit of grammatical niggling.

Language pedants [may believe in a] prohibition against “split verbs,” in which an adverb comes between an infinitive marker like “to,” or an auxiliary like “will,” and the main verb of the sentence....

Any speaker who has not been brainwashed by the split-verb myth can sense that these corrections go against the rhythm and logic of English phrasing....

In his legal opinions, Chief Justice Roberts has altered quotations to conform to his notions of grammaticality, as when he excised the “ain’t” from Bob Dylan’s line “When you ain’t got nothing, you got nothing to lose.” On Tuesday his inner copy editor overrode any instincts toward strict constructionism and unilaterally amended the Constitution by moving the adverb “faithfully” away from the verb.

I clicked there from Jim Lindgren's post. Pinker's op-ed mentions Lindgren and Lindgren's famous attack on the Texas Law Review Manual on Style — which was, when Jim attacked — just begging for the mockery he inflicted on it.

It's nice to note that the Framers of the Constitution didn't fall for the "split verb" urban legend. And it's funny to think about these 2 old law review editors face-to-face over an editing issue. Both Obama and Roberts served on Harvard Law Review and must have engaged in endless discussions of various points of editing. But let's remember that Barack Obama was the president of the Harvard Law Review — that is, the editor-in-chief — while John Roberts was the managing editor. For those of you who know law reviews, that means a lot. The managing editor is typically the person with the most intense interest in the details of grammar and usage. It would be cool if we could know that when Barack Obama paused after John Roberts moved the "faithfully" that he was thinking: I can see what you're up to, you old managing editor, and I know you are wrong.

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Apologies to all the great managing editors I have known whose knowledge of grammar and usage extends to the myths and urban legends that plague those earnest people who are trying too hard to get things right — hypercorrecting — and getting things wrong.