So, the original public meaning of the officer, and just to talk a little bit about what original public meaning is, is essentially the idea that the Constitution should be interpreted in light of how it was understood at the time that it was ratified or approved. If you're going to apply that methodology to officers of the United States, you might look and figure out what did Officers of the United States mean at the time?
The original public meaning, first of all, suggests, actually, that “Officers of the United States” was not a new term of art especially created for the Constitution. The phrase comes into being a few years before the Constitution is ratified, sometimes in reference just to Continental officers in the Continental army at the time, but there's never, during the drafting debates of the Constitution or the debates in the states about whether to ratify the Constitution, there's never a whole lot of discussion about what the phrase “Officers of the United States” specifically means. There's not really an indication that the drafters or the ratifiers thought that this was a new phrase that needed to be explained, or a new phrase that carved out an especially important class of officers.
The history, in terms of how the Constitution was drafted, actually suggests that the phrase “Officers of the United States” came into being to indicate that it wasn't going to just be officers in the executive department under the president who had to be subject to the Appointments Clause, but also judges who were appointed by the president with Senate consent, various ambassadors, and officials involved in foreign relations. So, the idea seems to be that officers of the United States broadened the category out beyond just officers under the president, and also, that it meant officers at the federal level, rather than at the state level.
There are some other times in the Constitution when the description of the United States is used in some of the other clauses, and sometimes the phrases used specifically in contrast to the phrase of the several states or of the states, again, giving more evidence that Officers of the United States probably just meant federal or national level officers. And then anybody who was that kind of official at the federal level would come under the Appointments Clause.