to boldly go and all that

Linguist Steven Pinker nails the explanation for chief justice Roberts's flubbing of the oath: he's internalised the widespread but unnecessary prohibition of split infinitives:

Instead of having Barack Obama “solemnly swear that I will faithfully execute the office of president of the United States,” Chief Justice Roberts had him “solemnly swear that I will execute the office of president to the United States faithfully.” When Mr. Obama paused after “execute,” the chief justice prompted him to continue with “faithfully the office of president of the United States.” How could a famous stickler for grammar have bungled that 35-word passage, among the best-known words in the Constitution? Conspiracy theorists and connoisseurs of Freudian slips have surmised that it was unconscious retaliation for Senator Obama’s vote against the chief justice’s confirmation in 2005. But a simpler explanation is that the wayward adverb in the passage is blowback from Chief Justice Roberts’s habit of grammatical niggling.