There’s only one real question heading into the CBS News Republican debate on Saturday: Can anyone stop Donald Trump?

The billionaire front-runner is coming off a big win in New Hampshire, has led polls in South Carolina for months, and enjoys an opposition that’s more divided than he could have hoped for, thanks to Sen. Marco Rubio’s debate choke and subsequent fifth-place finish in the Granite State.

The debate will be the best chance for everyone involved to either try to pry away Trump voters or build a coalition that can take him on in South Carolina, which votes February 20, and beyond. They have to do it quickly – if Trump is still winning primaries and the opposition is still divided three or four weeks from now, it will become extremely difficult to stop him from clinching the nomination or at least forcing a divided convention.

Trump, who occupied a similarly dominant position heading into last week’s debate in New Hampshire, responded at the time by laying low in the debate, sticking to his usual talking points about illegal immigration and trade, and avoiding gratuitous conflict. Close video History of dirty tricks puts candidates on guard in SC Joel Sawyer, former executive director of the South Carolina Republican Party, talks with Rachel Maddow about the state’s history of dirty campaign tricks and the Bush family history of success there. Joel Sawyer, former executive director of the South Carolina Republican Party, talks with Rachel Maddow about the state’s history of dirty campaign tricks and the Bush family history of success there. share tweet email Embed

When his campaign pulled a negative ad against Sen. Ted Cruz in South Carolina this week, opting instead for a play-it-safe run of positive spots, it looked like he would pursue the same strategy. But then he went on a Twitter rant against Cruz on Friday, even threatening to sue him over his eligibility to be president due to his Canadian birthplace. We’ll see which Trump shows up on Saturday night.

Cruz’s path to the nomination depends the most on him performing well in South Carolina and then a number of southern states on March 1. His campaign is already airing a tough anti-Trump ad targeting him over his failed attempt to take over an elderly widow’s home and turn the land into casino parking. Former Florida Gov. Jeb Bush hit Trump over the same story in the last debate.

Bush has accused his rivals of not taking on Trump enough in debates and on the campaign trail, while candidates and Trump critics have accused Bush’s super PAC Right to Rise of spending tens of millions on ads attacking contenders like Rubio instead. A new spot from the group targets Trump’s “liberal Democratic positions” and highlights his offensive statements against women and a disabled reporter. Close video Can the GOP establishment stop Trump, Cruz? The main event in South Carolina is between Donald Trump and Ted Cruz… but it’s also the last chance for the Republican establishment to stop Trump and Cruz. Can Jeb Bush, Marco Rubio or John Kasich rise to the challenge? The main event in South Carolina is between Donald Trump and Ted Cruz… but it’s also the last chance for the Republican establishment to stop Trump and Cruz. Can Jeb Bush, Marco Rubio or John Kasich rise to the challenge? share tweet email Embed

Rubio, who has mostly avoided getting in Trump’s way until recently, criticized Trump’s use of profanity and his lack of foreign policy knowledge this week, setting up possible points of confrontation in the debate.

“Negotiating a hotel deal in another country is not foreign policy experience,” Rubio said on Thursday.

The big problem, though, is that they all have as much reason to drag each other down as they do Trump. The assumption undergirding each campaign is that they can defeat Trump so long as they can narrow the race down to a one-on-one contest first. Surviving that long won’t be easy, though, especially if they don’t take some opponents out and fast.

If Bush or Rubio badly underperform in South Carolina, they could quickly fall out of contention. They also need to worry about Ohio Gov. John Kasich, who is not heavily contesting South Carolina but is broadly competing for mainstream Republican votes in their lane.

Rubio and Cruz are also still in a dogfight for conservative votes. Cruz’s campaign released a new ad this week targeting Rubio over immigration but pulled the spot after discovering an actress in it had performed in pornographic films.

With Trump more dangerous than ever, it’s possible the field gets over their collective action problem and tries to impress voters with their willingness to take him on. Or things could end up like they did in New Hampshire, where New Jersey Gov. Chris Christie (who has since left the race) beat up Rubio throughout the evening with a helping hand from Bush. The debate will be an important signal as to whether the field has changed its approach since Tuesday’s shocking primary.