I am working on connections with three presidents: Herbert Hoover, Richard Nixon, and Barack Obama.
My connection with the Hoovers is the most tentative out of all of them, and rests mostly on the identity of the mother of my 4th great grandfather, Jesse C. Hooven (Hooven-24). His father was a Nathan Hooven of Pennsylvania, and the identity of his first wife (the mother of my Jesse) has been unknown. While going through some Ohio marriage records, I found a marriage of Nathan Hooven (mis-indexed as Hoover) and Mary Ann Curtis that is a near perfect candidate to be the marriage record of Jesse's parents. Mary Ann Curtis was the daughter of John Curtis and Catherine Hoover (sister to Herbert Hoover's 2nd great grandfather John Hoover). I don't count this connection as anywhere near confirmed, as it's all based on circumstantial evidence. Mary Ann Curtis was disowned from her Quaker meeting for marrying out of unity, and my Jesse named his daughter Mary Ann, but besides some other naming coincidences I don't have much else to go on unless I am able to find someone named in a will. If I can confirm this Curtis connection, Herbert Hoover would be my 3rd cousin 5x removed. Not shown on WikiTree, as I haven't connected myself to the Curtis family due to lack of solid sources.
My relationship to Richard Nixon is as close to confirmed as you can get without DNA. My mother is a Mendenhall, and the Mendenhalls are perhaps my most well documented line. Richard Nixon's 2nd great grandmother, Martha Vickers, was the granddaughter of Joshua Mendenhall and Lydia Mendenhall, both descendants of the early Chester County, PA Mendenhalls. Through Joshua, we have common ancestors in Thomas Mildenhall and Joane Stroade, parents of the several Mendenhall siblings who immigrated. Lydia's father Aaron was the son of John Mendenhall and Elizabeth Maris - their son/Aaron's brother John is my ancestor. John and Aaron also married sisters, so we have a common ancestor there as well. He is my 7th cousin 3x removed, shown on WikiTree with (mostly) well sourced profiles. The Quakers make it easy to be confident. :)
I am fairly confident in my connection to Obama, though not as confident as the connection with Nixon. I would be related through his second great grandmother, Della Wolfley. The Wolfleys are well sourced through to their immigrant ancestor, Johann Conrad Wolfley/Wolflin (Wolfley-12). Professional genealogists (incl. those with Ancestry.com) have said that Johann Conrad is the son of Johann Martin Wolflin and Maria Margaretha Krafft of Baden-Wurttemberg. Their son, Johann Ludwig Wolflin (Wölflin-2) is my 8th great grandfather. My connection up to Johann Martin is confident and well sourced - I just need to find more sources on Conrad to confirm he is in fact their son. If so, Barack Obama is my 8th cousin 2x removed.