South Carolinians will head to the polls on Saturday to cast their ballots in the Republican presidential primary, as the state’s former governor, Nikki Haley, fights to hang on in a race still dominated by Donald Trump.

At her primary eve rally in Mount Pleasant, just outside of Charleston, Haley called on her supporters to turn out in large numbers on Saturday.

Related: South Carolina Republican primary: when to expect results and what they can tell us

“In a general election, you’re given a choice. In a primary, you make your choice,” Haley said. “This is the time we make our choice.”

But at this point, Haley would have to pull off a shocking upset to win South Carolina. According to the FiveThirtyEight average of South Carolina polls, Trump leads Haley by roughly 30 points in the state, and the former president has already won the first three voting contests in Iowa, New Hampshire and Nevada. At his own primary eve rally in Rock Hill, near the North Carolina border, Trump voiced robust confidence that he would deliver a decisive victory on Saturday and indicated he was already turning his attention to the general election fight against Joe Biden.

“We’re going to have a gigantic victory here in South Carolina,” Trump told thousands of supporters. “We’re going to show crooked Joe Biden and the radical left Democrats that we are coming like a freight train in November.”

Trump’s allies have expressed exasperation that the primary is continuing even though Haley has not yet managed to win a single state. Her best performance to date was in the New Hampshire primary last month, when she lost to Trump by 11 points. At an event in Charleston on Friday, Trump’s eldest son, Donald Trump Jr, told voters that the primary “should be over” and blamed Haley’s large donors for keeping her campaign alive.

“The billionaire donors that don’t actually care about conservative values but care about having a puppet in the White House will feed more money to the campaign to prolong the agony, to drag it out, to make it harder for us to get to the real fight, which is going after Joe Biden,” Trump Jr said. “So get out there tomorrow. Get all your friends. Let’s finish this thing strong because the stronger we finish, the faster we end it and the faster we can get to the main objective.”

Despite the tough talk from Trump and his surrogates, Haley’s team appeared undaunted in the days leading up to the primary. Haley has insisted she will stay in the race until Super Tuesday on 5 March, when 15 states and one territory will hold their primary contests. During a press call with reporters on Friday, Haley’s campaign manager, Betsy Ankney, announced a seven-figure ad buy across Super Tuesday states, indicating the candidate has no plans to drop out after Saturday.

“We know the odds, but we also know the stakes. And we think a whole lot of Republicans do, too,” Ankney said. “So we are going to continue to fight as long as we see that there is an appetite for our message, and so far, we’re seeing that there is.”

Speaking to the Guardian at Haley’s Mount Pleasant rally, congressman Ralph Norman, the only member of South Carolina’s congressional delegation to endorse Haley, justified her decision to remain in the race. He pointed to Haley’s well-attended campaign events as a sign that her message is resonating with voters, even if she falls short on Saturday.

“Obviously, you’d love to win. Single digits would be great,” Norman said. “But let the people decide. We can pull off a real upset in a lot of different ways.”

The Guardian’s Lauren Gambino contributed reporting from Mount Pleasant