hmm, what Presidential last names work best as first names, not McKinley or Hoover...

Kennedy Grant Garfield (although hard to imagine a guy named Garfield getting the Prez nickname) Fillmore? Jefferson Washington Wilson Jackson

also what ones would be commonly known presidential names and maybe the first thing one thinks of when hearing the name is the President - Kennedy for sure, but Grant is a common enough name that I don't think of Ulysses when I hear it.

My impression was that in the US, any surname can be used as a first name. Wasn't there even someone with Mackenzie as first name? Plenty of Harrisons, Taylors and other names that really don't sound like a first name.

Truman isn't too uncommon as a first name. Harry S. Truman was a president.