She has starred in the most frantically evasive campaign since Hannibal Lecter ran for president of the Vegan Alliance, but credit Theresa May for resolving one mystery.

If you were unsure about her political antecedents before she called the election, the Prime Minister has supplied the answer. During this extended edition of Who Do You Think You Are?, she has revealed herself as the political love child of Gordon Brown and Hillary Clinton. On this, she really has been very clear.

Which of her honorary parents is the stronger influence is hard to call, but the similarities to both are plain enough to negate any need for DNA testing.

Like Gordon, she became PM by acclamation early in a parliament after a record-setting stint at one of the allegedly great offices of state. And, like him, she was massively popular for a few months until the punters suddenly twigged her.

Six successful years at the Home Office (and survival in that ministerial abattoir counts as success) no more guaranteed she would grow into the top job than Gordon’s decade at the Treasury. Quite the reverse: the longer someone spends in one grand post, the more they are limited by experience and the less suited to the grandest post they become. Either side of the Attlee government, Anthony Eden spent almost 10 years as a greatly admired Foreign Secretary, and lasted less than two at No 10.

Theresa May reveals the naughtiest thing she's ever done

In a brave bid to escape her old man’s shadow, May took a gamble by going to the country. It didn’t seem a gamble at the time, though it might have done had a genealogist informed her that Hillary was her political mum (see below).

The decision that did Gordon in was not calling a snap election. In the autumn of 2007, a few months after succeeding Tony Blair, he had a healthy polling lead. But when George Osborne’s inheritance tax pledge narrowed that lead, he panicked. Gordon clucked it up. The chicken caricature stuck, and though he struggled on for almost three chaotic years, from that moment he was doomed.

So you understand May’s adolescent act of rebellion in doing the opposite by seeking a mandate of her own. But if she thought she had learned from dad’s mistake in not going to the country, she had failed to identify her mum’s lethal inadequacy.

Hillary Clinton also left a long spell in one of her country’s grandest political jobs, Secretary of State, with stratospheric approval ratings. She too should have won a general election at a canter against a candidate widely dismissed as too inexperienced, unpalatable and compromised by dodgy connections to be electable.

There were many reasons (misogyny, the post-Obama racist backlash, the hacked emails, a sense of abandonment among traditional Democratic voters) why Trump proved electable after all. But the primary reason was that Hillary was among the worst campaigners in global electoral history. Complacent beyond belief, riven by a sense of entitlement, an empty slogan-fixated orator of pulverising tedium, incapable of projecting empathy, twice as robotic as the Supreme Dalek… Does she begin to remind you of anyone?

The two qualities Hillary had in her favour were 1) not being her opponent, and 2) a reputation for stolid competence, though neither was as powerful a factor as she imagined. Fatally underestimating the appeal of a maverick rival promising change, Hillary hid herself away as far as possible in the assumption that she could coast to the line.

Again, does anyone else come to mind?

Jeremy Corbyn calls for Theresa May to resign

It remains a virtual impossibility that Hillary’s precise fate awaits Theresa May on Thursday. She cannot lose outright. But her limitations have been brutally exposed.

She has campaigned (in so far as she has bothered at all) in prose so staccato and stultifying it makes Dan Brown read like Dickens. Her implied response to the question of why she thinks she deserves power, à la Hillary, is that she bloody well does, and let that be an end to it.

If she has a vision for this country, as her earlier musings on social mobility suggested, she has kept it entirely to herself. As with Hillary and Gordon, the more she has been magnified beneath the campaign microscope, the smaller she has become.

Being an appalling campaigner doesn’t necessarily equate to being an appalling leader. Gordon, who probably did do more than anyone to rescue the world economy in 2009, would no more have punished the disabled for the sins of the bankers than called a referendum on leaving the EU. Hillary would have made a relatively sane, humane, able and progressive president.

The odds remain heavily on May getting the chance to prove that she inherited more and better from those two than secretiveness, paranoia, a craving for power, and the incapacity to speak like a humanoid life form. But if she does win decently and expects an eternally bloodthirsty parliamentary party to give her time to turn her reputation around, she cannot go on like this.