 Shortly afterwards, he was appointed Apostolic Nuncio to Ireland on November 27, 1951.In 1953 Paul Blanshard, author of "American Freedom and Catholic Power", unsuccessfully petitioned the U.S. Department of State to revoke O'Hara's citizenship because Blanshard believed that, as an American-born bishop with an American diocese working in Ireland, he was violating the McCarran Act by serving as an agent of a foreign power.On June 8, 1954, O'Hara was named Apostolic Delegate to Great Britain.