Donald Trump has a yuge problem in special prosecutor Robert Swan Mueller III. The American president’s anger at having this legal thorn in his administration’s side explains much of his recent erratic behaviour, as Daniel McCarthy explained in the magazine this week. Now we learn that Mueller is using a grand jury – a group that meets in secret and has the legal power to compel testimony – and that can only be an aggravation for Trump. He can keep saying it’s a 'Witch Hunt' – maybe it is – but a witch hunt could bring down his presidency, or at least make it impossible for his administration to function.

Mueller is trying to establish whether there was salty collusion between the Trump campaign and the Russian government over the releasing of emails that damaged Hillary Clinton. Even if he doesn’t find damming evidence, anything short of total exoneration (unlikely given Mueller’s conduct so far) could be deeply damaging to the Trump family, the Trump presidency, and, perhaps most importantly for Donald, the Trump business empire.

Which must be why the investigation is driving Trump wild. It’s certainly why he is so furious at Attorney General Senator Jeff Sessions, the man who caused the whole Mueller problem by recusing himself from the inquiry. It’s also why, as Daniel said, Trump appears to be trying to sack his way back to a successful presidency. He could sack Mueller, but that would make him look guilty as sin. As Pat Buchanan put it, Mueller has Trump in ‘a kill box’.