When it was discovered recently that Senator Obama had Irish forbears, it was assumed America’s Irish Catholic population would boost his campaign to become the first black president.

But further research into his family tree has shown that unlike Presidents Kennedy and Reagan, Mr. Obama’s ancestors came from the other side of the religious divide.

As the descendant of an Irish protestant family, Mr. Obama should not rely on the sort of support automatically enjoyed by Kennedy, whose presidency marked the political arrival of Irish American Catholics.

New research has traced Mr. Obama’s family tree back to his great-great-great-great grandfather Joseph Kearney, a well-to-do shoemaker from Moneygall, Co. Offaly, who lived between 1794 and 1861.

Mr. Obama’s roots were uncovered by Canon Stephen Neill, a Church of Ireland rector who found baptismal and marriage records in the house of a late parishioner, Elizabeth Short.

The presidential candidate comes from an Irish Anglican family, many of whom immigrated to the New World around the time of the famine and Ireland’s decimated potato crop in the 1840s.

The records show that Joseph’s brother Francis had already left Ireland and bequeathed land to his sibling in America on condition that he emigrated to inherit it.

“What I found was references to his relations and various grandparents in the records,” Canon Neill said.