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US Census Bureau's data shows that 35 million Americans claim Irish ancestry
As Barack Obama would testify, there are many good reasons to visit Ireland – a taste of real Guinness being one – but for US presidents there are 35m good reasons back home.
According to the US Census Bureau, 35 million Americans claim Irish ancestry, making them one of the two largest ethnic blocs in the country.
For Democratic leaders such as Obama, the attraction is all the greater since Irish Americans – clustered in the old manufacturing strongholds of America's east – have for more than 150 years been mainstays of the Democratic party, even if the link has subsided in recent years.
John F Kennedy was the first US president to visit while in office and the rapturous welcome he received confounded his advisers, who had argued against making the trip for fear that Kennedy would be seen as "too Irish" to voters.
Ronald Reagan made a successful visit in 1984 that played up his Irish roots and helped him appeal to the domestic Irish vote in an election year. In doing so Reagan erased the sour taste left from an unhappy visit in 1970 by Richard Nixon, who visited his ancestral home but appeared dull in comparison to the glamorous Kennedy seven years earlier.
Bill Clinton made the trip three times, playing a crucial role in the Northern Ireland peace process. Clinton's popularity proved that a lack of Irish roots – despite the best efforts of the White House to track down his most distant Irish relatives – didn't matter so long as the Guinness was being poured.
Clinton's celebration of Irishness rather than Ireland mirror the St Patrick's Day festivities celebrated throughout the US every 17 March, with greater brio than anywhere outside of Ireland itself.
As a character on the US version of The Office explains: "It is the closest that the Irish will ever get to Christmas."
