Republicans show they're ready to fight ahead of debate

New attacks launched ahead of tonight’s GOP... 02:40

Republican presidential candidates are gearing up for Saturday night's debate and signaling they're ready to punch first and punch back even harder, CBS News' Julianna Goldman reports.

What to expect at tonight’s GOP debate 03:55

The debate, the last before the key South Carolina GOP primary next Saturday, is hosted by CBS News and will take place in Greenville, South Carolina, beginning at 9 p.m. ET. Just six Republicans are still in the race, making the debate even more crucial.

Donald Trump has been the primary target of attacks in the Palmetto State, and now he's threatening to sue Ted Cruz over his citizenship if he doesn't pull his negative ads.

Campaigning Friday in Florida, Trump signaled he was ready for a fight Saturday night in South Carolina.

"They spend a fortune," Trump said. "They're spending money, you wouldn't believe it. It comes out of PACs, and who puts up the money? Special interests, special interests. Who else? Lobbyists."

Trump has come under fierce attack in South Carolina from rival Republicans and outside groups raising questions about his conservative values.

"There's nothing conservative about Donald Trump," a narrator says in a TV ad from the conservative Club for Growth.

"Look past the boasting, and you'll see right through him ... he supported partial-birth abortions," a narrator says in a different ad from Right to Rise, a super PAC supporting Jeb Bush.

Previewing Saturday's CBS News GOP debate 01:25

South Carolina is a state where faith is central to many voters.

Self-described evangelicals or born-again Christians made up 65 percent of Republican primary voters four years ago. While Cruz won the evangelical vote in Iowa earlier this month, Trump won it in New Hampshire.

Now the rest of the Republican field is trying to make inroads by proclaiming their beliefs.

"I think that life is divinely inspired," Bush said Friday in Anderson, South Carolina.

"I discovered my purpose by discovering the Lord," John Kasich said in a TV ad.

At a religious forum Friday, Marco Rubio and Cruz addressed the faithful.

"Faith is the most important influence in my life," Rubio said.

"I'm saved by grace, and it has transformed my life and my family's life," Cruz said.

But even as they highlight their faith, they're signaling that questions about Trump are fair game.

"I will take him on because he's not a conservative, and I don't believe he is a steady hand as a leader," Bush told Goldman. "... He's certainly an incredible entertainer. He has taken his reality TV status and taken it to new heights, but that's not what you need as a president of the United States."

Bush and other Republican candidates are seizing on Trump's penchant for profanity in the hopes that that won't sit well with South Carolina's religious voters. Viewers can expect to hear that line of attack on the debate stage Saturday night.