CHARLESTON, United States - Donald Trump and Nikki Haley were going head-to-head Saturday in South Carolina's Republican primary, with the ex-president poised to trounce his former charge in her home state and tighten his grip on the party's nomination.

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

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

But Trump made clear Saturday that he is looking beyond Haley to a likely November contest against President Joe Biden.

Speaking outside Washington to the Conservative Political Action Committee conference -- a must-stop for Republican politicians -- Trump spent much of his time bashing Biden, not Haley.

"A vote for Trump is your ticket back to freedom and your passport out of tyranny," he said.

"We have to break out of the nightmare that we are in and we have it in (our) grasp to make America richer and safer and stronger and prouder and more beautiful than ever before."

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

One Democrat, Caroline Palmer, said she could never support Trump. "I think he's a pretty terrible human being. And so I don't want any chance of him becoming president."

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

- Economy, migration -

Voters interviewed by AFP in South Carolina capital Columbia were complimentary about both candidates, although some criticized Trump for being divisive.

Husband and wife Jeff and Susan Stottler laughingly explained why they were not voting for the same candidate.

Jeff, 61, said Trump will "override everything that Joe Biden has done to put us in the economic and immigrant mess we're in," while Susan, 60, said her vote for Haley was meant to encourage Trump to pick her as his vice president.

While Trump -- who faces four criminal indictments -- tightens his hold over the party, Haley has sought to focus on the "chaos" that she says follows him everywhere.

On Saturday, she lashed out at comments he had made to a group of Black conservatives in the state.

Nodding to his multiple indictments, Trump said 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.

Haley responded: "It's disgusting. But that's... the chaos that comes with Donald Trump."

- Haley hangs on -

In common with Democrats, Haley has been hitting Trump over his outlook on the international stage and oft-voiced admiration for several authoritarian leaders.

She has blasted Trump's reaction to the death of Russian dissident Alexei Navalny -- he avoided criticizing President Vladimir Putin -- and his threat to encourage Moscow to attack NATO nations not meeting their financial obligations.

But Haley's central argument has been that polling shows her performing better than Trump in hypothetical matchups with Biden.

She has vowed to compete in the Republican primary through "Super Tuesday" -- when multiple states vote on March 5 -- regardless of what happens in South Carolina.

Though the 52-year-old Haley trails Trump badly, analysts say she is building her profile for a potential 2028 run -- and is poised to step in should legal or health problems knock the 77-year-old Trump out of the race.

"Nikki Haley's an incredible role model," said one Republican voter, Julie Taylor. "She's not giving up, she's showing strength and grace and courage."