For a while – four years in fact – it looked as though Hillary Clinton had put the past behind her. As America’s top diplomat, she enjoyed by far the highest ratings of any US figure. Her popularity abroad was matched by appreciation at home for the grace with which she buried the hatchet with Barack Obama. Americans most admire politicians who seem to be above politics. Mrs Clinton had a taste of that. Then she quit as secretary of state (to prepare for her second White House bid). She has been losing altitude ever since. The worry among Democrats is her woes are only a foretaste of what is to come. They are probably right.

Like almost every Clinton “scandal”, there is less than meets the eye to revelations that Mrs Clinton used a private account for her official emails. The discovery that she routed her government correspondence through a “homebrew” server is the kind of exposé that sends Washington into a tailspin but barely registers beyond. From the Whitewater investigations during Bill Clinton’s presidency in the 1990s to the ructions over the 2012 Benghazi murders of four US diplomats, the smoking gun is always just beyond reach. Failure to find one is why Whitewater prosecutors were sidetracked into Mr Clinton’s dalliance with Monica Lewinsky. It is also the path by which the Benghazi probes stumbled on Mrs Clinton’s home server.

With the Clintons there is always some cover-up waiting to be unearthed. Nearly a quarter of a century of probes — from Little Rock to Washington — have failed to bring them down. Yet there is also more to “homebrew” than meets the eye. Mrs Clinton was technically within the law in using a private account. It is possible her home server was more secure than the State Department’s porous system. None of this really matters. To Mrs Clinton’s enemies, the fact that a trove of private emails exist is invitation to conspiracy. It is also an example of how she plays by different rules. Even President Obama uses official email. Mrs Clinton’s pursuers are unlikely to give up until every one of her emails has been subpoenaed.