The Ruling Stewards of Gondor were descended from Mardil (sp?) the good steward. They were a family of noble Dunedain who had escaped with Elendil, Isuldur and Anorien from the wreck of Neumenor. However they were not related to the line of Elendil. (There is some circumstantial evidience that they had been vassals of the Lords of Anduie (sp?), Elendil's family fief in Numenor.)
Moreover, the family had married into non-Dunedain families and was not pure bred. Nevertheless, Gandalf comments on several occassions that the blood of Numenor ran almost true in the veins of Denethor and Farimir, though not so much in Borimir.
Neverthelss, despite his mixed blood, Borimir was clearly a follower of the ethics of the Dunedain and was big on the whole "We men of Godor are truth speaker. ... We boast but seldom and then peroform or die in the attempt. ... I would not even trap an orc with a falsehood. ..." thing (quotes from Farimir's discussions with Frodo in Ithilien).
Dunedain don't lie. Fallen Dunedain do (a.k.a. Black Numenoriens) do.
Maybe Bush is a descenent of Castimir the Usurper? Kinda makes sense when you think about it...