Who will Haley voters support in Trump-Biden election?

Nikki Haley ended her failed bid for the White House much like she spent the final weeks of campaigning: with a warning for her former Republican rival.

"It is now up to Donald Trump to earn the votes of those in our party and beyond it who did not support him," she said, pausing. "And I hope he does that."

The former South Carolina governor's coalition of Trump-resistant Republicans and independents was simply too small to stop Mr Trump's march to the Republican nomination, which was all but assured after a commanding series of victories on Super Tuesday.

But that same coalition - a mix of moderate, college-educated and suburban voters who helped her win two primary races - now hold considerable power. The question now coming into focus, with serious implications for the presidential race, is who they will pick in November.

Ms Haley's exit effectively marks the start of the 2024 general election, which is now all-but-certain as a rematch of four years ago between Mr Trump and Democrat Joe Biden. And this time, experts say, the path to the presidency runs through the voters Ms Haley left behind.

"They are the ones who are going to decide this election," said Republican strategist Kevin Madden.

And both Mr Trump and Mr Biden know it. Ms Haley's announcement on Wednesday was followed immediately by statements from both candidates, making their appeals. Mr Trump invited Haley supporters "to join the greatest movement in the history of our nation", while Mr Biden said there was "a place for them in my campaign".

Experts say Ms Haley's voters fall roughly into the three categories: never-Trumpers, independents, and Republican Party loyalists.

For that first segment of Ms Haley's camp, their direction is slightly more clear: far away from Mr Trump.

In interviews with these voters throughout the campaign, many explained their support for Ms Haley entirely as a rejection of the former president.

"Trump is a cancer in the Republican Party," said Holt Moran, a South Carolina Republican who left the party in 2016 when Mr Trump became the nominee. "He's just a disaster for this country."

On the campaign trail, many of these voters barely mentioned Ms Haley herself, talking instead about Mr Trump's mounting legal challenges, the 2020 US Capitol riot, and what they described as his contempt for democracy.

Few thought Ms Haley could actually beat Mr Trump but they cast their ballot for her anyway - a true protest vote which experts say indicates the depth of their animosity.

Voters like these have given Democrats some reason for optimism.

Some polls from early voting states suggested a "large percentage" of Haley voters were open to voting for Mr Biden, says veteran Democratic strategist Simon Rosenberg. Among Haley voters in North Carolina, for example, only 21% said they would vote for the Republican nominee "no matter who it is".

For the Republican party, "these are very bright, red warning signs", Mr Rosenberg said. "The Republican party has splintered… and Haley is now showing that that splintering is a legitimate and serious thing."

But so far, Mr Trump and his allies have seemed uninterested in making a sincere effort to draw Haley voters in, instead lobbing increasingly personal attacks at her in speeches and interviews.

Even after she dropped out, Mr Trump offered no olive branch. He mocked her losses, saying in a statement she was "TROUNCED... in record setting fashion" before offering his tepid invitation to her supporters to unite behind him.

Politically, "it's pure idiocy", Mr Rosenberg said. "The party can't win elections without their full Republican coalition."

But other analysts have cautioned that a general dislike for Mr Trump among Haley-supporting Republicans will not necessarily translate to a vote for Mr Biden in November. Partisan ties do not break down so easily.

"That's not the norm," said Democratic strategist Kate Maeder. "Because our politics today are so tribal, there's a very slim majority in the middle that is still persuadable."

That's been true for past rivalries within the main political parties: outright defectors are rare.

Soon after Hillary Clinton ceded the Democratic presidential nomination to Barack Obama in 2008, nearly one-third of her supporters said they would vote for Republican John McCain instead. By election day, 82% had cast their ballots for Mr Obama.

Even as her attacks against Mr Trump grew more pointed and more personal, Ms Haley herself stuck to the line that Mr Biden was the more dangerous candidate. By doing so, she has left herself space to say she remains loyal to the Republican Party, no matter the nominee.

Mr Biden's own political weaknesses will also play a role, said Republican analyst Whit Ayres.

"A lot of Haley voters don't want Biden either," he said, pointing to the president's low job approval ratings and growing concern among voters that he is simply too old to run.

Dozens of Haley voters have also said just that in interviews over the last few months. They wanted to move on from Mr Trump, but could not see themselves voting for Mr Biden, who they described as weak on the border and bad for the economy.

"For so many years now we've had to vote for the lesser of the two evils," said lifelong Republican and Haley supporter Tim Ferguson.

"I can't vote for Biden," he said. "I will vote for Mr Trump again, and I won't feel any better about it than I did last time."

Mr Ferguson's unhappiness is widespread.

According to a February poll from Morning Consult, 19% of the American electorate are considered "double haters" - those who are unhappy with both Mr Trump and Mr Biden. Some analysts suspect that this sort of apathy may stop many of those voters from casting a ballot at all.

"This is the match-up that nobody wanted," said Mr Madden, the Republican strategist. "I think the bigger risk is that they stay home."

Changes to the US economy, developments in Ukraine and in Gaza, or simply an embarrassing gaffe by either Mr Trump or Mr Biden, could all sway independent-minded voters. And the outlook is further complicated by Mr Trump's many legal challenges. Polling suggests he would lose some Republican voters if he was convicted in any of his four criminal cases.

Jim Sullivan, a Republican from Indiana, said while he would not cross party lines for Mr Biden, he was still undecided. A true double hater, he does not like Mr Trump either, but sees no other option. "I'm wrestling with that," he said.

With eight months left until Mr Biden and Mr Trump face off again, experts agree it is simply too early to know for sure where voters like Mr Sullivan will land.

"The real answer to every single question is this is going to be really close, and we don't know yet," Mr Madden said.