Todd Harrison of the Centre for Strategic and Budgetary Assessments, a non-partisan think-tank in Washington, estimates that from 2013 to 2022 Mr Romney’s commitment would add up to $2.3 trillion of additional expenditure. If the increases were made gradually during Mr Romney’s first term, as Romney officials suggest, the figure would come down to $2 trillion. Mr Harrison points out that the base defence budget has not been 4% of GDP since 1992, in the aftermath of the cold war. Even during the administration of George W. Bush, defence spending “only” went from 2.9% of GDP in 2001 to 3.7% in 2009. Over the past 20 years the base defence budget has averaged 3.3% of GDP. Mr Harrison says: “What you spend on defence really should be a function of your security needs, what you think the threat environment is and what you think you need to protect the country. It shouldn’t be a formula based on the size of your economy.”