If the president gets married in the first 50 pages, you're reading a What Kind of President Was He? biography. These get the formative years out of the way as quickly as possible, and generally eschew the personal details throughout. The Madison biography, I think it was, mentioned Dolly for the first time by saying "he was married at this point."
If the president gets married after the first 50 pages, you're reading a What Kind of Man Was He? biography. These take the time to build a character portrait. I prefer these because I am a woman and I like to empathize with people.
Margaret Leech married off McKinley with all haste so she could get right to the war stuff, which is kind of strange because her Garfield biography was the opposite.
This is just a miscellaneous McKinley fact, as are the following:
Look at how many conservatories used to take up the White House lawn. They had orange trees and all that.