Nikki Haley, who as ambassador to the United Nations when Mr Trump was in office, spent the day lambasting her former boss as the South Carolina Primary voting got under way.

But in what was almost essentially a silent swipe at Ms Haley, Mr Trump mentioned only President Joe Biden as he focused on a likely match up between the two.

‘You’re fired!’

Donald Trump is set to sail to victory in the primary in Ms Haley’s home state of South Carolina on Saturday evening (Sunday, lunchtime AEST).

He has won every primary held so far with every rival, aside Ms Haley, dropping out.

But Ms Haley has said she will stay in the race, at least until “Super Tuesday” on March 5 when a slew of states reveal their preferred candidate.

The vote in the solid red state is of particular importance because it has historically revealed the eventual Republican presidential nominee.

Mr Trump didn’t spend the day campaigning in South Carolina, instead it attended the Conservative Political Action Committee conference in Maryland.

“To achieve our future, we have to throw off the chains of the political class, and that begins with crooked Joe Biden,” the former president said to a friendly crowd.

“That begins with telling him: ‘You’re fired!’” Mr Trump said, echoing his catchphrase of US show The Apprentice that helped cement his fame.

To applause he said Mr Biden was “most incompetent president in the history of our country”.

He also touched upon his mounting legal troubles declaring he was a “dissident”.

“I’ve been indicted more times that Alphonse Capone”.

Notably, last week, it took Mr Trump several days to acknowledge the death of Russian dissident Alexei Navlany who Teh Kremlin has been widely accused of ordering the death of.

‘It’s disgusting’

Mr Trump added that, “Black people like me because they have been hurt so badly and discriminated against, and they actually viewed me as I’m being discriminated against”.

He said Black voters also particularly liked a now-famous mug shot taken of him in a Georgia jail.

It was comments that Ms Haley, who voted in South Caroline with her elderly mother, seized upon.

“It’s disgusting, but that’s what happens when he goes off the teleprompter. That’s the chaos that comes with Donald Trump.

“That’s the offensiveness that’s going to happen every day between now and the general election, which is why I continue to say Donald Trump cannot win a general election. He won’t”.

Ms Haley was a popular governor of the state before becoming Mr Trump’s UN ambassador in 2017, but her old boss is backed by the local party establishment and nearly two-thirds of voters in opinion polling.

Ms Haley lost the first four nominating contests to Mr Trump who is looking to continue his unbeaten 2024 primary streak. A victory by Mr Trump over his last remaining major GOP rival would further add to his momentum toward the party’s nomination.

Since the early nominating contests in Iowa and New Hampshire in January, the rhetorical fire has intensified between the two as the primary narrowed into a two-horse race.

Ms Haley has urged voters to ditch the “chaos” that follows the ex-president, though that message has not won over voters in polls held so far in Iowa, New Hampshire, Nevada and the US Virgin Islands. She is hoping her home state can help fuel a comeback.

She has also called for a “new generational leader that focuses on the solutions of the future instead of all the issues of the past.”

Despite being a popular former governor in the southeastern state, she’s down in polling by some 30 points ahead of Saturday’s vote and Mr Trump is expected to win. However, she has said she is determined to stay in the race, even if she loses in South Carolina.

Underscoring his confidence, Trump told his supporters on the eve of the vote: “Honestly, we’re not that worried.”

But seeking to demonstrate that he is looking beyond Ms Haley, Mr Trump is already sizing up a rematch against Mr Biden, as no serious Democrats are challenging the incumbent president.

“We’re going to win this state and then we’re going to tell crooked Joe Biden, ‘You’re fired,’” he said.

“We are coming like a freight train in November (the general election will be held).”

How primary votes are awarded

South Carolina has 50 Republican delegates and will award the votes of 29 of them to the candidate who wins this primary. It will also award three to the winner in each of the state’s seven congressional districts.

A minimum of 1215 delegates are needed nationwide to secure the Republican presidential nomination – more than half the 2429 available. After three state contests so far, Ms Haley has 17 delegates to Mr Trump’s 63.

South Carolina’s delegates are a sliver of the total number, but wins in early primaries and caucuses have historically created momentum leading up to Super Tuesday, the day when most of the states vote. This year, Super Tuesday is on March 5, and 16 states will choose about one-third of all delegates. They include California (169 delegates) and Texas (161).

In remarks released early to the US media, Mr Trump will say in a speech later Saturday that “if we can break out of this Biden nightmare, we have it in our grasp to make America richer, safer, stronger, prouder and more beautiful than ever before.”

Polls in the southern US state opened at 7am local time (11pm AET) and will close 12 hours later.

South Carolinians do not have to indicate party allegiance when they register to vote, and are allowed to have their say in either the Democratic or the Republican primary.

Mr Haley – a more traditional conservative who espouses limited government and a muscular foreign policy – will hope for votes from moderates, but the tactic did little for her as she lost to Trump in each of the first four nominating contests.

Trump – who faces four criminal indictments – is tightening his hold over the party as he pushes toward a second term in the White House.

Ms Haley has sought to focus on the “chaos” that she says follows Trump, predicting that his total outlay on court cases this year could top $100 million ($A152m).

“Everything he touches is chaos that leads to a loss,” she said on Saturday.

“How many more times do Republicans have to lose before they realise that maybe he’s the one that’s the problem?”

Haley refuses to quit

In common with Democrats, Ms Haley has also been hitting Mr Trump over his outlook on the international stage and oft-voiced admiration for the leaders of the world’s most authoritarian regimes.

She has blasted Mr Trump’s reaction to the death of Russian dissident Alexei Navalny – in which he avoided criticism of President Vladimir Putin – and his threat to encourage Moscow to attack NATO nations that had not met their financial obligations.

But Ms Haley’s central argument for months has been that polling shows her performing better were she to go head-to-head with Joe Biden.

– With AFP