Back in May 2012, Barack and Michelle Obama made a state visit to the UK that involved the usual photo-friendly rigmarole such as wreath-laying and Beefeater-inspecting. They also spent the night at Buckingham Palace and attended a state dinner in their honour where Obama gave a short speech and toast to the Queen. Journalists, however, noticed something unusual about the man who is one of the most eloquent politicians of all time: he was nervous.