Some say Bill Clinton sees his wife’s bid for the White House as a referendum on his own legacy. Others that his controversial appearances are really a well- executed plan to “mess with Barack Obama’s head”. Still others that he is driven by the need to atone for marital transgressions by doing all he can to ensure that the former first lady makes it into the Oval Office.

All three may help explain what is surely the most prominent cameo role to have featured in any US presidential campaign. But anyone who latches on to the former president’s frenetic schedule in South Carolina is left in little doubt that he is following a script that fits with Hillary Clinton’s relentlessly on-message campaign. And it has a familiar “It’s the economy, stupid” ring to it.