Josh Mandel was a rising star in the US Republican party.

After watching the young former Marine and grandson of a Holocaust survivor address the Jewish Federations of North America in 2005, a local Democratic operative later recalled thinking, “this guy is going to be the first Jewish president”.

Thanks to Donald Trump, however, Mr Mandel’s ascent came to brutal, shuddering halt earlier this month.

For months, 44-year-old Mr Mandel had been at the head of the Republican pack in the much-watched race to become the party’s Senate candidate in Ohio in November’s mid-term elections. The seat – currently held by the retiring GOP senator Rob Portman – is a relatively safe one, especially with the Democrats expected to take a pounding thanks to Joe Biden’s dismal approval ratings.

Mr Mandel, however, ended up badly losing the primary to JD Vance, the best-selling author of “Hillbilly Elegy” and a former venture capitalist-turned-born again populist.

Once viewed as a bellwether – Ohio backed the winner in every presidential election from 1964 to 2016 – the state is now firmly Trump country. The former president carried it by a comfortable eight points in both 2016 and 2020.

For Republicans jockeying to stand for this plum Senate seat, therefore, Mr Trump’s endorsement was a prized one. Mr Mandel – whose TV ads contained the tagline “Pro-God, Pro-Guns, Pro-Trump” – had indeed loyally trooped to Mar-a-Lago last spring to pay homage at the court of King Donald.

Certainly, Mr Mandel’s campaign has pushed all the Trumpian buttons. “Melding conspiracy theories and white grievance politics,” in the words of the New York Times, the Republican hopeful theatrically burned a mask; railed against Mr Biden’s supposedly “Gestapo”-like vaccine and testing mandates; and blamed the “deep state” for, among other events, the pandemic, Black Lives Matter protests and 6 January insurrection at the US Capitol. He called for “government schools” to be shut down with children educated in churches and synagogues. And he warned Afghan refugees would “bring child brides and Sharia Law to your neighborhood”, suggesting – Orban-like – that the billionaire philanthropist George Soros was financing an “invasion” of migrants across the southern US border.

Perhaps most importantly, Mr Mandel worked effortlessly to demonstrate his absolute fealty to Mr Trump. He peddled the former president’s myths about the “stolen” 2020 election and described himself as Mr Trump’s “number one ally” in Ohio. Mr Mandel even wheeled out Mr Trump’s short-lived National Security Adviser, Lieutenant General Michael Flynn, on the campaign trail.

To ram home the message, two conservative pressure groups which backed Mr Mandel splashed close to $1m in attack ads contrasting their candidate’s loyalty to Mr Trump with Mr Vance’s past heresies. A self-professed “Never Trump” Republican in 2016 – he called Mr Trump “noxious”, “reprehensible” and an “idiot” and hinted he might vote for Hillary Clinton – Mr Vance had morphed into a fully-fledged MAGA convert by 2022.

Like much of the Republican party, Mr Mandel has, of course, been on something of a political journey himself over the past decade – albeit not, perhaps, one as dramatic as that of Mr Vance. In the Ohio state legislature, to which he was elected in 2006, Mr Mandel built a reputation as a pro-business, moderate conservative; a proclaimed proponent of civility in politics, he touted his willing to work across the aisle with Democrats. With the rise of the Tea party during Barack Obama’s presidency, however, Mr Mandel began to tack to the right. His successful 2010 bid to become state treasurer and unsuccessful 2012 Senate race saw a more aggressive, partisan political persona emerge. And Mr Mandel fell in behind Mr Trump in 2016 even if his support was, like many other Republicans, both belated and somewhat lacklustre.

But – despite prostrating himself before the MAGA movement since its 2016 triumph – Mr Trump’s endorsement never came. Instead, barely three weeks before polling day, the former president weighed into the race on behalf of Mr Vance.

Mr Trump’s backing boosted Mr Vance by 12 points in the polls, lifting him from third place to first and allowing him to slip ahead of Mr Mandel as the campaign entered its final strait. As Rex Elsass, a Republican strategist in Ohio, suggested after Mr Vance’s 8-point win on polling day: “If the whole issue in the campaign is who is most Trump-like, expect it to work against you when you don’t get the endorsement.”

So why did Mr Trump – who prizes loyalty and hates to back a loser – seemingly take such a gamble by throwing Mr Vance a last-minute political lifeline?

It can’t have hurt that two prominent Trump acolytes - tech billionaire Peter Thiel and the hard-right Fox News anchor Tucker Carlson - were already firmly on Team Vance.

The former president will also no doubt have admired Mr Vance’s willingness to tell tales – he claimed, for instance, that the Biden administration was allowing fentanyl into the country because of its potential to kill “a bunch of MAGA voters in the middle of the heartland” – so tall that even he might have struggled to construct them.

And, as if to prove the wisdom of his choice, Mr Vance spent the final weekend of the campaign out and about with two of Mr Trump’s biggest cheerleaders – and most controversial members of Congress – Marjorie Taylor Greene and Matt Gaetz. The pair gleefully stuck the knife into Mr Mandel, with Ms Taylor Greene declaring: “I didn't see the sincerity there. I didn't see the authenticity. I just saw someone that learned to speak MAGA and just repeat it over and over.”

That said, Mr Trump himself gave every impression that – once given – his endorsement of Mr Vance wasn’t something he’d given much subsequent thought to. “We’ve endorsed JP, right? JD Mandel, and he’s doing great,” he absent-mindedly asked someone off stage during a rally in Nebraska shortly before Ohio voters went to the polls.

Perhaps, then, the real parable of Josh Mandel is the impossibility of winning the support of a man as whimsical and unpredictable as Donald Trump.

Having inspected the candidates, Mr Trump reportedly decided that Mr Mandel was “weird” and didn’t have the right “look”.

Political careers and fortunes in Trump’s Republican party, it seems, now rest on such profound judgments.