Mr Obama and Mr Cheney share a French ancestor

Lynne Cheney said she had discovered while doing family research for a new book that her husband and the Illinois senator were eighth cousins.

She said she traced a common ancestor of the two men to be a 17th century immigrant from France.

She described the connection as "amazing".

"This is such an amazing American story that one ancestor... could be responsible down the family line for lives that have taken such different and varied paths."

According to Mrs Cheney's spokeswoman, Mr Obama is distantly related to Mareen Duvall, whose son Samuel married the granddaughter of Mr Cheney's ancestor, also called Richard Cheney.

Mr Obama's spokesman, Bill Burton, responded to the news by saying: "Every family has a black sheep."

Mr Cheney, the brooding neo-conservative closely associated with the decision to invade Iraq, has little else in common with Mr Obama.

Mr Obama, the son of a Kenyan man and a white woman from Kansas, has earned epithets like "rock star" because of his popularity among young Democrats, and a reputation as a liberal because of his voting record in the Senate.