CHARLESTON, South Carolina — Republican presidential candidates Marco Rubio and Jeb Bush are locked in a bare-knuckled fight for third place in a South Carolina primary vote Saturday, afraid that anything less could blunt their White House hopes.

With front-runner Donald Trump fighting to hold off U.S. Sen. Ted Cruz of Texas and win his second straight early nominating contest, Rubio and Bush are battling to become the main anti-Trump alternative from among establishment Republicans seeking the party’s nomination for the Nov. 8 election.

An NBC News-Wall Street Journal/Marist poll released on Friday showed Trump in the lead with support from 28 percent of likely Republican primary voters, followed by Cruz at 23 percent. Rubio led Bush narrowly, 15 percent to 13 percent.

The Bush-Rubio competition is layered with home-state drama: Bush, 63, is the elder statesman of Florida politics having served as governor. Rubio, 44, is the upstart understudy, a first-term U.S. senator who served in Florida’s legislature.

Rubio supporters were offended by the millions of dollars in attack ads spent by Bush’s Super PAC, Right to Rise, believing that the money would have been better spent attacking Trump rather than trying to undermine a like-minded Republican.

“People are going to do whatever they think they need to do to win. But it’s notable they spent far more money attacking Marco than they have the front-runner Donald Trump,” said Rubio spokesman Alex Conant.

The Bush team dismissed the complaints.

“I don’t think there’s anything personal about it from Jeb’s side,” said Jim Dyke, Bush’s campaign chief in South Carolina. “Jeb for good reason feels like he’s much more qualified to be president of the United States. That’s what this is all about.”

Bush has a key backer in South Carolina’s Republican U.S. senator, Lindsey Graham, but Rubio upped the ante by winning the support of popular Gov. Nikki Haley.

Her endorsement gave Rubio momentum at just the right time and the two have campaigned together around the state.

Rubio is treading carefully around whether Bush should exit the race if he performs poorly in South Carolina, saying Bush has worked hard and “has a right to be in this race as long as he wants to be.”

“I mean, he’s spent $50 million attacking me. If there are differences in policy we’ll talk about it. What I’ve said about Governor Bush is he doesn’t have any foreign policy experience, which is true. But I don’t view that as an attack. I view that as a fact,” Rubio told reporters Wednesday.

Bush has bristled at the charge, telling supporters he has visited 89 countries and seen his brother and father develop foreign policy as U.S. presidents.

His team has made much of Rubio’s having missed many hearings and votes as a member of the Senate Foreign Relations Committee.

“It’s hard for me to be lectured to by a gifted young guy who thinks going to committee hearings means you know something about the world,” Bush said.

Rubio forces had wanted to knock Bush out of the race in the New Hampshire primary, but a bad Rubio debate performance and a strong campaign trail performance by Bush thwarted those hopes with Bush edging his rival for a fourth-place finish.