That's the worry of a growing number of people close to Ted Cruz's campaign, who are privately beginning to fear that a big loss in South Carolina to Donald Trump on Saturday could signal more defeats to come in the so-called SEC states that are the lynchpin of Cruz's strategy.

"If they're pretty far back from Trump and they can't get southern conservative evangelicals in South Carolina, I do think they're probably going to have a hard time elsewhere," said Erick Erickson, a conservative writer in touch with Cruz's team. "I sense a real fear from people that if Trump blows everybody out of the water in South Carolina, that he is suddenly unstoppable."

Cruz's team once envisioned South Carolina as a rubber match between Trump, the New Hampshire victor, and Cruz, the Iowa winner. Now, it's being read as an omen of what's to come in 10 days' time when Southern states vote on Super Tuesday.

Cruz once called the God-fearing, gun-toting SEC states that vote then on March 1 his "firewall," but polls show Trump leading in South Carolina, and a dominant performance Saturday would show that Cruz has not been able to sufficiently consolidate the evangelical base that he needs to win down the road in places like Tennessee and Georgia.

The recent CNN Poll of Polls shows Trump with an average lead of 16 percentage points over Cruz, though a new NBC News/Wall Street Journal/Marist survey on Friday showed Cruz only 5 points back.

Several people close to the campaign concede that losing South Carolina by double digits would spell serious trouble for Super Tuesday. If it's a tighter loss, some say, it would validate the theory that Trump was susceptible to their attacks and encourage more.

"Everybody is watching: Can support be stripped from Donald Trump?" one pro-Cruz fundraiser asked, predicting that if Trump only earns between 25% and 30%, it will "unleash" a new wave of anti-Trump money. "Then people will realize Trump can be beaten in a lot of the March 1 states."

"But if Trump gets 38 or 40 -- and Cruz is second with 22 or something like that -- it's going to be very ominous," the fundraiser added.

All week, Cruz has campaigned with the same urgency seen in the lead-up to Iowa, gleefully drawing sharp contrasts with Trump and Rubio alike. He has rolled out his best endorsements, including one from Rep. Mark Sanford on Friday. And he has showed an awareness of the high stakes on Saturday for his campaign, where the narrative could begin to swing against him in the South.

"Twenty-one hours. That's how long we've got until the polls close," Cruz said in Myrtle Beach. "These next 21 hours are going to decide a great deal."

Importance of SEC primary

Cruz allies are doing everything they can to separate their candidate's fortunes in South Carolina from those elsewhere in the South.

The campaign points to a national NBC/Wall Street Journal survey this week that showed Cruz leading Trump by 2 points, although other national polls still have the New York businessman easily in the lead. They also maintain that Trump's position on abortion and his recent comments about the presidency of George W. Bush will doom him in the South.

"It's a little tough to do an exact extrapolation between what happened in South Carolina and on March 1," said Jason Miller, a senior Cruz adviser, who stressed that Cruz has already proven in Iowa that it can turn out his voters. "These are states that Ted Cruz matches up well in."

Cruz surrogate Jack Kingston, a former congressman from just over the border in Georgia, went so far as to tell reporters Thursday that Cruz "shouldn't even be viable" in South Carolina, quite the departure from a state that Cruz's team once saw as winnable.

It is hard to overstate the importance of March 1 to Cruz's self-professed path to victory -- he has made the date, which will award more delegates than any other day in the Republican calendar, the cornerstone of his strategy.

Allies tell CNN Cruz is hoping to win 60% of the delegates there. He scrapped time in Iowa to take two barnstorming bus tours of the south. He's called his operation three to five times better than the rest of the field's. And the core of Cruz's SEC stronghold, his home state of Texas, is still unlikely to be pierced.

Fighting Rubio and attacking Trump

The Cruz campaign appears as occupied with Marco Rubio leapfrogging them into third place as it is with catching Trump for first. It releases anti-Rubio attack ads at a daily rate and has jumped squarely into a messy, seemingly endless argument with Rubio's over Facebook pages and Photoshopped images

Miller and Cruz aides are trying to hoist Rubio's expectations as high as possible: Given Rubio's endorsements here, including Gov. Nikki Haley, Cruz's team argues Rubio needs to outright win the state in order to meet them.

As for Trump, the plan is simple: attack.

With the race shifting to a national campaign defined more by expensive television ads than retail politics, some Cruz supporters have faith that South Carolina will show that negative ads like those Cruz forces have aired against Trump will work. After largely skating free in Iowa and New Hampshire, Trump is finally being attacked by a battery of super PACs.

Cruz's campaign is hitting Trump on those issues, airing ads featuring Trump's 1999 interview with the late Tim Russert in which he declares he is "pro-choice." (Trump maintains his position has changed and sent Cruz a cease-and-desist letter, which Cruz laughed off.)

Assuming Cruz does hold off Rubio, though, the key will be how large the margin of loss is to Trump, who also holds a large lead in Nevada.

"If Trump wins and we're second, the SEC primary becomes a 50/50 scenario," said one Cruz insider. "It's our territory, but he'll have the momentum."

In the meantime, Cruz is trying his best to look ahead. When a foreign-born woman who now lives in Georgia crossed the Carolina border to see Cruz in Greenville on Thursday, Cruz was as eager to get her to the ballot box as she was herself.

"The reason I became an American citizen is so I can vote for people like you," Hannah Kanner, born in communist Czechoslovakia, told him. "I'm from Georgia -- sorry! I wish I could vote on Saturday, but I can't."

"On March 1," Cruz replied, "you can."