Supposedly, an estimated 10 percent of Americans can trace their ancestry back to the Mayflower.Not surprisingly, former President George W. Bush — son of a president, grandson of a U.S. senator, first offspring produced by the marriage of the blueblooded Bush and Walker families — is a Mayflower descendant. President Barack Obama’s roots go almost that deep: He is a descendant of Thomas Blossom, who arrived in Plymouth Colony less than a decade after the Mayflower landed.America’s two most recent presidents are distant cousins. But what distinguishes them from most of the rest of us is merely their ancestors’ earlier time of disembarkation, and maybe the place from where those ancestors initially departed.