The revelation that Barack Obama's ancestors can be traced to the small village of Moneygall in Co Offaly was greeted with surprise and resigned amusement at the time. Another American president with vague links to an ancestral Irish cottage.
But it soon became clear that this one was different. However unlikely it seemed, the connection was real. There are no gaps in the chain. A detailed family tree can be followed, generation by generation, from Barack Obama's mother all the way back to the Kearneys in Moneygall.
But exactly who were the Kearneys who went to America at the end of the 18th century and what happened to them when they got there?
That question is fully answered for the first time in a new book by Stephen MacDonogh. It's called Barack Obama - The Road from Moneygall and it tells the extraordinary story of the Kearneys in America in exhaustive detail.
The first to go was Thomas Kearney from Moneygall, who was born in 1765, emigrated probably in the 1780s and arrived in the port of Baltimore, Maryland, where he got married in 1791.
Thomas is listed in the Baltimore Directory for 1800 as a carpenter. Some time later he went west, travelling a few hundred miles before settling in a wild, densely-forested valley in what would eventually become the state of Ohio.
Probably the most evocative pictures in MacDonogh's book are of the Kearney gravestones in Compton Cemetery in a townland called Wayne, in Fayette County, Ohio.
One of the best preserved gravestones, with inscription still legible, is that of another Thomas Kearney, a nephew of the original emigrant.
The inscription tells us that this younger Thomas was born in the King's County (Offaly) in 1800, and died in Ohio in 1845.
Another headstone is that of Thomas's brother Francis who had also followed his uncle to America. Francis died in 1848 and in his will he left some land to another brother, Joseph, who was still back in Moneygall, on condition that he came out to America to work it.
What makes the book so fascinating is not just the way it brings Obama's Irish ancestors to life. This is not just the story of one family, it's the story of how America was made, starting before the American Revolution and following the creation of the country by the pioneers who moved out from the east into the frontier to settle the land. It's a story of hardship, courage and great adventure.
Almost in passing, the story also brings up many facts about Irish and American history that are often forgotten.
Although the assumption is often made that nearly all Irish emigrants to America were Catholic, the Kearneys were Protestant.
In fact, when Thomas Kearney was born, a quarter of the population of Ireland was Protestant and in cities and towns this went up to 30-40%.
Up to half a million Irish Protestants emigrated to America in the same decades as the Kearneys and played a pivotal role in the creation of the new nation.
More Irishmen (nine) signed the Declaration of Independence than any other ethnic group and all but one of them were Protestant. The main Catholic wave of emigration came later, in the decades after the famine.
Many of the Protestant settlers were as poor as the Catholics that followed them. Thousands of them from Ulster who were admirers of King Billy (William of Orange) settled in the Appalachian mountains and became known as the Billy Boys of the Hills, or Hillbillies. Daniel Boone and Davy Crockett were from the same stock.
But then, as MacDonogh points out, our habit today of referring to John F Kennedy as the first Irish American President is wrong. He was the first Catholic, but at least eight presidents before him were Protestant Irish, all the way back to the iconic Andrew Jackson (both of whose parents were Irish).
The history of the Kearney family in Ireland is also an instructive window into the past. Originally from Tipperary, as well as the Moneygall Kearneys, there was a Dublin branch of the family that was highly successful, including a John Kearney who was Provost of Trinity College Dublin and later Bishop of Ossory and a Michael Kearney, who was a businessman and became embroiled in the Dublin city politics of the day.
The fortunes of the Dublin part of the family were founded on the wig-making trade, a huge business at the time because professional people wore wigs instead of washing their hair with water which often spread disease. Wigs were also worn by the gentry and the aristocracy. But the Act of Union in 1800 and the transfer of all official business to London killed the trade in Dublin.
The Kearneys no longer prospered as a result and this, and the worsening situation in the country in the years before the Famine made them look elsewhere.
America beckoned. America, where 160 years after Joseph Kearney arrived as an immigrant in 1849, his great-great-great-great grandson became president.