The real threat to Hillary Clinton’s pursuit of the US presidency is not Donald Trump, but the FBI. I’ve held that view all along, and I still hold it, even though the Bureau has decided not to prosecute her for mishandling classified government information – for anyone who’s switched off US politics these last few months, the great email affair was her use of a private email server for official business when she was Secretary of State.

So Hillary has been spared the ultimate disaster: a criminal indictment that would surely have forced her to end her candidacy. But the fall-out from the email scandal isn’t over – and had she been running against any other opponent than Trump, it might well have proved fatal.

Here is a candidate, whom voters already consider slippery and untrustworthy, being publicly criticised by the head of her own government’s top law enforcement agency for having been “extremely careless” in her handling of government material. For good measure James Comey, the FBI director, suggested it was possible, indeed likely, her email had been hacked by a hostile state or agent, quite possibly both.

All that saved Clinton was the fact that the investigating agents could find no evidence of intent. If so, one can only conclude that this supremely experienced politician, who prides herself on her competence, didn’t know what she was doing.

FBI director says 'no charges' for Hillary Clinton amid email scandal

Daily, she castigates Trump for his recklessness, his lack of judgement, and a temperament that disqualifies him from the country’s top job. Now whose judgement is lacking? Daily, she refers to her record as senator and Secretary of State as proof that she’s perfect presidential timber. Really, if she can’t even follow the rules for protecting government secrets? Who’s reckless now?

Offered this sort of present four months before election day, any other Republican opponent would have cashed in. He would be mentioning it every day, the airwaves would be flooded with attack ads, and campaign surrogates would have been spreading the message to every corner of the land. Not Trump.

Yes he’s weighed in on the issue, tweeting away about “Lying Crooked Hillary”. But then he’s quickly spoiled the effect by claiming the episode proves the entire US judicial system is rigged, even that Attorney General Loretta Lynch, head of the Justice Department of which the FBI is part, had been bribed by the Clintons.

The problem is that if there’s a straight arrow in US government, it’s Comey. He was a top federal prosecutor before serving as deputy Attorney General during the last Republican administration, but who in 2004 prevented top Bush officials from getting the then Attorney General John Ashcroft to sign off on an extension of the government’s secret domestic wiretapping programme.

Hillary Clinton testifies before House Select Committee on Benghazi Show all 17 1 /17 Hillary Clinton testifies before House Select Committee on Benghazi Hillary Clinton testifies before House Select Committee on Benghazi Saul Loeb/AFP/Getty Hillary Clinton testifies before House Select Committee on Benghazi Pete Marovich/Bloomberg/Getty Hillary Clinton testifies before House Select Committee on Benghazi Saul Loeb/AFP/Getty Hillary Clinton testifies before House Select Committee on Benghazi Andrew Harrer/Bloomberg/Getty Hillary Clinton testifies before House Select Committee on Benghazi Saul Loeb/AFP/Getty Hillary Clinton testifies before House Select Committee on Benghazi AFP/Getty Images Hillary Clinton testifies before House Select Committee on Benghazi Andrew Harrer/Bloomberg via Getty Images Hillary Clinton testifies before House Select Committee on Benghazi Andrew Harrer/Bloomberg via Getty Images Hillary Clinton testifies before House Select Committee on Benghazi Evan Vucci/AP Hillary Clinton testifies before House Select Committee on Benghazi Democratic presidential candidate, former Secretary of State Hillary Rodham Clinton testifies on Capitol Hill in Washington, Thursday, Oct. 22, 2015, before the House Benghazi Committee. (AP Photo/Carolyn Kaster) AP Hillary Clinton testifies before House Select Committee on Benghazi Carolyn Kaster/AP Hillary Clinton testifies before House Select Committee on Benghazi Saul Loeb/AFP/Getty Hillary Clinton testifies before House Select Committee on Benghazi Carolyn Kaster/AP Hillary Clinton testifies before House Select Committee on Benghazi Saul Loeb/AFP/Getty Hillary Clinton testifies before House Select Committee on Benghazi Saul Loeb/AFP/Getty Hillary Clinton testifies before House Select Committee on Benghazi Chip Somodevilla/Getty Images Hillary Clinton testifies before House Select Committee on Benghazi Saul Loeb/AFP/Getty

And he wasn’t exactly tender on Clinton in the extraordinary statement he delivered on Tuesday to announce the FBI’s decision not to recommend prosecution. You can argue (and some former Justice Department officials already have) that he grossly exceeded his remit in delivering his “extremely careless” verdict about Clinton’s behaviour.

The right course, they argue, would have been to have simply put out a statement that after due investigation (in this case lasting 12 months) the FBI had decided not to seek a prosecution. And that would have been that. Except that in this overheated political moment, it wouldn’t have been that. Comey would surely still have been summoned by Republicans to a Congressional committee hearing to explain himself on live TV.

That’s what happened on Thursday. It was a nakedly partisan occasion, with Democrat members of the panel lobbing softballs, and Republicans trying to elicit further damaging comments from Comey for use in future attack ads – or, however improbably, to show him up as a craven tool of the Democratic establishment.

On both counts they failed. But the email saga will run and run. Lynch is to face a Senate committee next week to explain why she agreed to a 30-minute private meeting with ex-president Bill Clinton, a few days before the Bureau was about to conduct its interview with his spouse. Both insist that it was just a catch-up chat between two old friends, grandchildren and all that. But as a recklessly inappropriate encounter that could be perceived as an attempt to subvert the course of justice, it takes some beating.

Meanwhile Republicans are trying to stop candidate Clinton from receiving national security briefings (as is the norm for the two candidates in the final weeks of a campaign). Further down the line, if she does win the White House, security clearances for some of her closest aides could now be problematic.

Most serious, the whole episode feeds into negative public perceptions of the Clintons. Look at her previous comments on the subject – you are reminded of the expert lawyer she is, slicing and dicing the facts, at each instance giving the least possible ground, rarely lying outright, but always, as they say, economical with the truth.

Next, what about those thousands of “personal” emails she erased from her private server? Were these really exclusively personal? And the entire email saga raises yet again the issue of how the Clintons seem to treat the law as something that applies to other people, but not them. Where they are concerned, even Trump’s bluster against a “rigged” judicial system starts to ring true.

The email affair raises memories of Clinton scandals past, whether real or imagined. After decades of political harassment by Republicans, almost all of it unmerited, you can understand her caution and her obsession with privacy and why she risks so little. Whatever she lets out, she feels, will come back to bite her. But the whole thing has Americans wondering whether they really want another four years (or eight) of the Clinton psychodramas.