Like all good theatrical productions, a prime minister's visit to Washington should offer moments of high drama and ripe comedy. Think of Tony Blair addressing an electrified Congress after 9/11. Or the Reagan White House briefing against Neil Kinnock minutes after he’d left the Oval Office. Or the moment when Boris Johnson asked Bill Clinton about his sex life. Or that time Cherie Blair's hairdresser was left behind at Camp David, and a helicopter had to be sent to rescue him.