In the Clinton case, FBI Director James Comey decided after an investigation that she had been careless in using a private server but it was not intentional.

Mr Trump is also accused of obstructing the investigation. But he says Mrs Clinton destroyed evidence and points to the deleted emails. At one press conference, he even urged Russia to find them.

In Mr Comey's view there was no cover-up, even though an FBI investigation found many of the deleted emails were work-related.