As I understand it, "President's day" is intended solely to remember Washington's birthday. While doing a little research, I came across what seems to be a surprisingly comprehensive explanation of the entire issue, but there's a catch...it was written by Snopes. Sometimes they do okay, but overall they are liberal. Does anyone know if this article is true? 
According to them, it was actually the New York Times which introduced some confusion by implying Lincoln was included. This seems like an interesting tidbit, and they do quote the NYT, though I cannot currently access the actual issue to which they are referring (August 18, 1968, p. 25).
Thanks! --David B (TALK) 20:36, 17 February 2019 (EST)