Martin Van Buren, 8th President of the USA - Descendancy from King John of England

That´s because you hit, the only exception/ president, which doesn´t follow suit. Van Buren.
He´s a descendent of Stephen (i think, the 3rd/ III), too.
http://en.wikipedia.org/wiki/List_of_U.S._presidential_relatives

https://realitybloger.wordpress.com/tag/plantagenet-line-of-preside...

http://familypedia.wikia.com/wiki/Genealogical_relationships_of_Pre...

http://weareallrelated.com/presidents-family-tree-chart/

http://www.geni.com/path/Theresa+Ren%C3%A9e+El%C3%A9na+Delgado+Toss...

apparently, it´s Stephen I
From an email, I wrote about 6months ago.

"These lines seem to be greatly researched, as connected and connecting Presidents of the United States. More to the relationships of the Presidents of the US can be attained through, http://www.weareallrelated.com

And BridgeAnne d'Avignon, who has formerly confirmed my relationships to all of the Presidents of the US, including Martin van Buren, through Stephen I."