A little research today found another potential cousin. (Three if we go back another generation to Rev John Smith's inlaws, Samuel and Sarah Soole Hinckley.)
The source is Ancestors of American Presidents, Gary Boyd Roberts, 2009 edition. Gary Boyd Roberts is a senior research scholar for the New England Historic Genealogical Society, and is highly trusted in the field. So I feel comfortable saying, if I can prove my descent from John Smith, I'm cousin to President Obama. (As well as to the individuals in the left-hand column.)
[If I do the math correctly: President Obama's 8th great-grandparents are my 7th great-grandparents, so we're 8th cousins once removed, and my sons would be 9th cousins. George HW's 9th great-grandparents are my 9th great-grandparents, so we would be 10th cousins.]
William Addams Reitwiesner was also a highly respected researcher. He passed away in 2010, but also conducted some research on Obama. He stated that Samuel Smith and Elizabeth Pierce had other descendants:
Samuel Smith m. Elizabeth Peirce .Susannah Smith m. James Pitney .Benjamin Pitney m. Abigail Byram |.Sarah Pitney m. Mahlon Pitney (below) | .Mahlon Pitney m. Lucetta Banks Cooper | .Henry Cooper Pitney m. Sarah Louisa Halstead | .MAHLON PITNEY (1858-1924), US Supreme Court Justice, m. Florence Theodora Shelton | .Beatrice Louise Pitney m. Horace Rand Lamb | .Barbara Pitney Lamb m. Franklin D'Olier Reeve | .CHRISTOPHER REEVE (1952-2004), actor .Elizabeth Pitney m. Caleb Swayze |.Daniel Swayze m. Bethia Horton | .Mehitable Swayze m. John Leonard Sliker | .John Leonard Sliker m. Nancy Johnson | .Renzila Sliker m. Alfred Allen Seguine | .Margaret Seguine m. Benjamin Kinsey | .Alfred Seguine Kinsey m. Sarah Ann Charles | .ALFRED CHARLES KINSEY (1894-1956), entomologistI already considered Kinsey a cousin through my Stoughton descent, but Reeve is new information.
All the links in my ascent from Mary [Pitney] Swayze to Rev. John Smith of Barnstable are confirmed by Roberts and Reitwiesner except the initial link - that Mary Pitney was the daughter of Susannah and James Pitney.
Susannah and James' daughter Elizabeth married Caleb Swayze, a brother of Israel Swayze, Mary's husband. I'd say the odds are good, but I don't have a source to cite yet besides a few online sites I've found which all cite in turn the generic 'Online Family Trees.'
But this is a link I definitely want to be true.