Initially Gilmore was in favour of the 2008 first Lisbon Treaty referendum. When it was lost, he declared that the "Lisbon Treaty is dead". According to a wikileaks cable dated 23 July 2008 and released in 2011, he told the US Ambassador privately that he would support a second referendum. The Ambassador reported that: "He explained his public posture of opposition to a second referendum as 'politically necessary' for the time being". In 2009, the Lisbon Treaty proposal was passed by the Twenty-eighth Amendment of the Constitution of Ireland.