Occasionally in the news I have heard that the President or Vice President has sworn in some new appointee. According to my Black’s Law Dictionary, the POTUS is the supreme magistrate of the land, so it seems there’s nothing illegal or unconstitutional about this. Still it seems odd. Have sitting Presidents or VPs ever done this in the past?
Or does the authority to swear in new appointees rest in their status as officers of the United States?
SFAIK there’s a constitutional or statutory (depending on the office) requirement that the office-holder should take the oath, but there’s no legal requirement that it should be administered by anybody, or taken in the presence of anybody. It makes sense that the oath should be taken in the presence of reputable witnesses, so that afterwards there should be no question about whether the oath was taken or not, but the whole business of the oath being administered by a judge (or anyone else) appears to be entirely ceremonial, and to have no legal significance.
I think that the swearing-in of junior officials by the P or the VP is being done in the capacity of being their ultimate supervisor; it’s akin to an executive order. AFAIK, the President cannot administer oaths more generally outside the executive branch. That’s a judicial function (which is why couples can go to the courthouse to get married, but not the White House).
The reference to the President as a “supreme magistrate” strikes me as some sort of obsolete locution, as no one now conceives of the President as a judicial officer.