But Haley cannot be enjoying the physical threat that comes with the campaign. A few weeks ago she asked for Secret Service protection because of escalating threats and harassment.

Yet Haley still refuses to yield and “kiss the ring” of Trump, as she put it: “We don’t do coronations in America.” The Trumpite clamour that she quit the contest would make the Republicans a “Soviet-style” operation with just one candidate, Haley says.

She insists that the party needs her because while Trump may be able to win the nomination, he is fated to lose the general election against President Joe Biden.

“I’m the one that saves the Republican Party,” Haley posits. “I think my message has broken through. Not only are we getting Republicans, we’re getting independents, we’re getting Reagan Democrats – the people who want the anger to stop, the people who want the division to stop and the people who want us to stop having 80-year-old candidates.”

There are four chief reasons that she might be insisting on running an unwinnable race.

First, she might be positioning in the hope that Trump anoints her as his vice-presidential candidate. She hasn’t ruled it out. “She would definitely help Trump” if she were on his ticket, says Green, because she appeals to different demographics, notably educated women, traditional Republicans, independent voters and even some Democrats.

A Fox News voter analysis found that 59 per cent of Haley’s voters say they wouldn’t vote for Trump even if he is anointed as the Republican nominee.

“But to be his running mate, you have to absolutely affix your lips to Trump’s ass, and I think Nikki is too proud to put up with that,” Green says.

Second, she could be entrenching herself as the leading Republican back-up should Trump be locked up. “There is no way that the American people are going to vote for a convicted criminal,” says Haley. If so, she seems to want to be ready to replace him as Republican nominee. Asked directly if this were her plan, she refuses to answer directly.

Or third is the intriguing speculation that she could run for the presidency as an independent. She points out that a majority of Americans, around 60 per cent, consistently reject both Trump and Biden for the next term in the White House. Running as an independent candidate would allow Haley to appeal to this these voters. Asked directly, Haley only stoked the speculation by saying that she was running as a Republican “right now”.

If she were to stand as an independent, “she’d probably peel more votes away from Trump than Biden, but that’s not a given,” says Green.

One potential as a vehicle for an independent Haley might be a newly prominent non-profit called “No Labels”. Calling itself centrist and non-partisan and with a $US70 million war chest, No Labels says it is “definitely” interested in talking to Haley as the group’s possible presidential pick.

This implies that she’s a centrist. But Haley could only be considered a centrist by way of comparison to Trump and right-wing extremists. She’s more of a traditional conservative Republican and opposes abortion, for instance. And the logistics and expense of getting an independent candidate on the ballot in all 50 US states in time for the election is daunting.

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Fourth, she might be angling for the 2028 presidential election, building profile and support. Already, she has done unexpectedly well. “Don’t discount that I defeated a dozen fellas,” she reminded an interviewer, referring to all the other Republican contenders bar Trump.

Mike Green says: “My guess is she’d be more effective as a never-Trumper outside, not running. Her narrative is resonating, more than that of former Republican senator Liz Cheney, who was too strident, and former New Jersey governor Chris Christie, who was too fat and yesterday’s news, Haley is a more credible spokesperson for the never-Trumpers, reminding sceptical Republicans why they don’t like Trump.” If so, that would make her a post-Trump candidate.

“In another election or two she could be a credible candidate for the White House.”

If recent US politics offers us one lesson, it is that anything is possible.

Peter Hartcher is international editor.