Washington DC - Donald Trump wants to "bully" his way to the Republican presidential nomination, his sole remaining challenger Nikki Haley said Sunday, as she accused the party leadership of seeking to declare him the nominee prematurely.

Haley lost the Iowa caucuses and the New Hampshire primary but has vowed to stay in the contest, despite Trump's insistence – backed by some top Republican Party leaders – that the race is over.

"He can't bully his way through the nomination," Haley said on NBC's Meet the Press.

Haley noted that the nominating process was still in its earliest stages – Republicans have voted only in Iowa and New Hampshire so far – and suggested that Trump had pressured the Republican National Committee (RNC) to back him much too soon.

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"You can't do that based on just two states," she said.

The former South Carolina governor took particular aim at the RNC for throwing the national party's support – and resources – behind Trump soon after the New Hampshire vote.

The voters' will was "very clear," RNC chair Ronna McDaniel told Fox News on Tuesday. "We need to unite around our eventual nominee, which is going to be Donald Trump."

But with 48 states yet to vote, Haley told NBC, "I don't think this is the place of the RNC... I think that Trump overstepped when he pushed them to do it."

Haley suggested that she expected to stay in the race at least until so-called Super Tuesday on March 5, when voters in 16 states and US territories cast ballots in what can be a decisive exercise.

The next Republican primary is in Haley's home state of South Carolina on February 24. But most Republican legislators there have thrown their weight behind Trump, and polls suggest he could defeat the former governor by an overwhelming margin.

Haley intimated on NBC that even a loss there would not necessarily knock her out of the race, saying she simply needed to do better than she had in New Hampshire, where she lost to Trump by 11 points.

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"We're going to keep on going and see where this gets us," she said. "I take it one state at a time."

Haley also brushed aside suggestions she might be staying in the race in hopes that Trump's many legal problems, or perhaps his health, might leave an opening for a challenger.

"I've never stayed in this race because of court cases," she said.