US presidential hopeful Barack Obama turns out to be a distant relative not only of President George W. Bush but also of wartime British prime minister Winston Churchill, according to US researchers.

The New England Historic Genealogical Society traced the family trees of the three major presidential candidates, also revealing Democratic rival Hillary Clinton's ties to pop icon Madonna and Beat generation writer Jack Kerouac.

"You'd think with all that singing talent in the family she'd be able to carry a tune," Clinton's senior adviser Philippe Reines said. "But now it makes much more sense how she snagged a Grammy."

Clinton won for best spoken word Grammy in 1997 for "It Takes a Village."

And while Obama and Hollywood heartthrob Bard Pitt are ninth cousins who share a relative who died in 1769, Clinton is a ninth cousin twice removed of Pitt's partner Angelina Jolie, sharing a common ancestor who died in 1718.

Clinton is meanwhile also related to a number of celebrities with French Canadian ancestry, including singers Celine Dion and Alanis Morissette.

"It is common to find people of French Canadian descent to be related to large numbers of other French Canadians," said genealogist Christopher Child, who conducted the research.

On the Republican side, John McCain's family tree came up with perhaps less surprising results, revealing mainly that he was a sixth cousin of First Lady Laura Bush.

Other ties established by the genealogical society linked Obama to former presidents Gerald Ford, Lyndon Johnson and Harry Truman, and to Civil War General Robert Lee.