Washington:

She abandoned her White House ambitions two months ago, yet Nikki Haley is still taking a significant chunk of votes in presidential primary contests -- underlining a persistent refusal among a sizable bloc of Republicans to get behind Donald Trump.

In his latest victory over Haley in Indiana on Tuesday, the polarizing tycoon romped home with 460,000 votes -- but he only notched 78 percent support, an underwhelming tally for a former president essentially seen as an incumbent.

In Marion County alone, the highest populated part of the state that includes Indianapolis, Haley won 35 percent -- a particularly sobering outcome for Trump, given that his rival dropped out after the March 5 "Super Tuesday" primaries.

"It's hard to imagine Republican voters in deep red Indiana are that passionate about Haley's non-candidacy," Kaivan Shroff, a strategist on Hillary Clinton's 2016 election campaign, told AFP.

"What is more likely is this signals a protest vote against Trump. These voters want to be clear they are not happy with the Republican nominee and they are humiliating Trump in these primaries to prove it."

She would likely balk at the allusion, but the tenacity of the Haley vote has prompted several US media outlets to refer to her ongoing presence on the primary stage, long after the curtain came down, as a "zombie campaign."

She has not endorsed the 77-year-old former president and told supporters after dropping out that "it is now up to Donald Trump to earn the votes of those in our party and beyond it who did not support him."

Inroads

But Trump has failed to make inroads with Haley's moderate support, and she has continued to pick up a small but significant vote share ahead of the Republican nominating convention in July.

In a comfortable majority of the states and territories that have weighed in so far in the Republican primary, Trump has fumbled more than a fifth of the electorate.

He lost Vermont and Washington DC outright, and his vote share in a further eight contests was under two-thirds, ahead of an election in November that will be fought on the margins, with almost every vote likely to count in many districts.

Barring a major, campaign-killing convulsion for Trump, Haley has no chance of resurrecting her candidacy.

But the primaries have laid bare Trump's key shortcoming -- his lack of appeal among the moderates, independents and voters with college degrees he will need to prevail against President Joe Biden.

The Biden campaign -- wary of its own problems with a coalition of progressives angry over the president's backing for Israel's war on Hamas in Gaza -- has been reaching across the aisle.

It released a TV spot last month targeting the suburban battlegrounds with the message: "If you voted for Nikki Haley, Donald Trump doesn't want your vote."

Scorched-earth rhetoric

Trump has shown little sign of moving to the middle since emerging as the Republican presidential pick, and his increasingly extreme, scorched-earth rhetoric at his campaign rallies seems unlikely to woo Haley supporters.

"There's a lot of talk about how Biden's coalition is threatened by his support for Israel, but not enough about the distaste for Trump among a significant number of Republicans," said Donald Nieman, a political analyst and history professor at Binghamton University in New York state.

"That dislike -- it's more appropriate to call it disgust -- for Trump and his antics hurt Republicans significantly in the 2022 mid-terms, and it is shaping up to be the unreported story of 2024."

It's not all bad news for Trump, of course.

Moderate conservative publication The Bulwark tempered Democratic delight over the Indiana result in an editorial Wednesday, pointing out that Trump has been a shade ahead in polling averages for months, and that Biden's push to narrow the gap has stalled somewhat.

Meanwhile, Nicholas Higgins, a political science professor at North Greenville University in South Carolina, cautioned against reading too much into the "open" Indiana primary, where non-Republicans were allowed to vote.

"This will become clearer in the next two weeks as Maryland and Kentucky hold closed Republican primaries," he said.

"If Haley continues to get 15 to 20 percent of the votes in those closed primary states it's indicative that Trump has a problem in the Republican base."