A New Form of Originalism

Steve Calabresi has a Letter to the Editor in the WSJ arguing that Section Three cannot apply to Donald Trump because Trump was not "an officer of the United States" under that provision. Why does he believe that? Because he thinks that the term "officer of the United States" did not apply to the President in the original Constitution. What about the evidence that the original public meaning of the term was different in 1868? My understanding is that Professor Calabresi considers that evidence irrelevant.

I'll leave this debate to the originalists, but I must admit that I've never heard of this form of originalism before. I thought that we were supposed to ascertain the original public meaning of the words when ratified. A prior legal understanding (what Jason Mazzone and Cam Tecimer call "interconstitutionalism") informs the original public meaning, but that cannot be the end-all and be-all.

UPDATE: Professor Calabresi now has a post on Volokh laying out his view in greater detail. He does not think that the evidence from 1866-1868 is irrelevant, but he does think that it is inadequate. I'm not sure, though, whether he is aware of how much evidence there is.