A year ago, Rishi Sunak was the runaway favourite to be the next Tory leader, with Liz Truss polling only a third of his support. He started the contest in front in surveys of members and won the parliamentary stage of the race comfortably.

Polls now put Truss miles ahead. And while the voting by Conservative Party members, less than 1 per cent of the British electorate, does not end until early September, some 9 in 10 say they have already made up their minds.

What happened?

Or, rather, what part of whip-smart, decent, teetotalling, hard-working, married-to-his-sweetheart, fiscally responsible and small-c conservative do Tory members not like?

An American colleague wondered whether Britain is just not ready for a prime minister from an ethnic-minority background (Sunak’s parents immigrated from India). That is a fair question, although I don’t think race is a significant issue here.

As Boris Johnson said bitterly in his last parliamentary address, “when the herd moves, it moves”. A cynic would say that Cabinet hopefuls among MPs have hopped off the fence to the side where the grass looks greener. Even Penny Mordaunt, who was eliminated in the parliamentary stages amid allegations that the Truss camp had leaked damaging documents, has now rowed in behind the front-runner. But that explains the momentum, not why it has gone Truss’s way.

One obvious factor is the person not in the contest — Boris Johnson. His own MPs ended the affair after a series of scandals, but many party members have had second thoughts. Johnson’s supporters portray Sunak’s resignation as the event that tipped the scales against the Prime Minister. Sunak has had a hard time shaking his casting as Brutus to Johnson’s Julius Caesar. Many Tories clearly struggle with the idea of handing the crown to the man who wielded the knife.

Another ghost haunting Sunak the candidate is Sunak the chancellor. It is very difficult for a Conservative former chancellor who raised taxes — to the highest level in four decades — to campaign as a tax-cutter. There is also a sense that he raised the wrong taxes — his national insurance increase hit both working people and their employers — that he made the system much more complex, and that he did not manage to fund reforms of social care. Many conservatives also suspect that he is perhaps a little too dogmatic and too deferential to the Bank of England, whose mandate Truss wants to revisit.

“He’s too clever by half” is a comment you hear from Conservatives, which pretty much dooms a candidate.

On an emotional level, Sunak’s message of fiscal responsibility has not matched well against Truss’s Johnsonian message of optimism amid all the grim news. Truss makes it all gloriously, improbably, simple: slash taxes, borrow where needed and watch growth return. She dismisses as “not inevitable” the prolonged recession that the Bank of England has forecast. She has managed to position herself as the successor of Johnson’s Brexity boosterism while also the candidate of change.

This may be the first leadership campaign in many years that has not focused on Europe, but Brexit still looms in the background. The Right of the Tory Party thinks Sunak’s more emollient style and desire to avoid further strain on the economy will lead to compromise over the Northern Ireland Protocol, which Johnson was determined to rewrite. They have thrown their backing behind Truss, who declares that the only language Europe understands is the language of strength. That backing filters through to the party’s grass roots and, crucially, helped to win her the support of the two newspapers that matter most to this selectorate: the Telegraph and The Daily Mail.

Sunak’s tactics have often seemed all wrong for this race; more suited to a General Election. Announcing a plan to cut VAT on fuel just looked like Truss-lite. A pledge to cut income tax in seven years looked out of touch when people are worried about energy bills in seven weeks.

Outside the economic portfolio, he looked less comfortable than Truss. Pledging to expand the definition of extremism to include those who “vilify Britain” was intended to look tough on crime, but looked tough on free speech instead. Telling voters in affluent Tunbridge Wells that, as chancellor, he changed funding formulas that had “shoved all the funding into deprived urban areas” so that “areas like this” can get more funding was Christmas come early for the Labour Party’s social-media team.

Truss’s name used to get an eyeroll in the Westminster bubble. But as polling expert and University of Strathclyde Professor John Curtice told Spectator TV, “Liz Truss’s narrative is working — the empathetic, ordinary girl who grew up in Paisley and went to a comprehensive school.”

Rishi’s narrative, by contrast, now seems to work against him, which was not the case a short time ago. As one of the youngest-ever chancellors and a rising star in the party, he was referred to affectionately as “Dishy Rishi” (British slang for a man who is attractive). He wrote the cheques that kept people afloat during the pandemic. Now his first name sounds too much like “rich”, which he is. His expensively tailored suits and his wife’s tax status make him seem far less relatable when so many face a cost-of-living crisis. That he once held a US green card — which meant he pledged to eventually live in the US — before returning it when he was chancellor, still gets cited as a reason to withhold trust.

Truss has made a few campaign mistakes, but so far they have not mattered. She has nearly achieved Johnson escape velocity.

It’s important to note at this stage that the contest is not over. Sentiment can shift. The Bank of England’s dire warnings could give Tories pause about plumping for Truss’s positivity over Sunak’s sombre warnings. Being so far ahead so early in the voting can backfire. Still, it seems the Tories have all but named the next prime minister and it’s not to be Sunak, the immigrant’s son. The only question is whether they will come to regret it.

• Therese Raphael is a columnist for Bloomberg Opinion covering healthcare and British politics. Previously, she was editorial page editor of The Wall Street Journal Europe