For the Democratic presidential candidates, tonight’s debate in South Carolina is critical. It’s their final face-off before the state’s primary and Super Tuesday, when voters in 14 states will head to the polls.

It’s also a big night for ViacomCBS, as it’s the first debate of this cycle hosted by CBS News. In addition to airing on the broadcast network, it will air on BET, and stream live from Charleston, S.C. on CBSN, CBS News’ free 24/7 streaming news service and on Twitter via @CBSNews. It’s the first major television event to broadcast simultaneously on CBS and another network within the ViacomCBS portfolio.

In the political context, its timing is “key,” says Face the Nation moderator and CBS News senior foreign affairs correspondent Margaret Brennan. “To have this many candidates still in the race, I think you're going to see a lot of elbows thrown because they know how high the stakes are.”

Brennan will join in the debate questioning alongside CBS News’ chief Washington correspondent Major Garrett and 60 Minutes correspondent Bill Whitaker. Norah O’Donnell, host of CBS Evening News, and Gayle King, co-host of CBS This Morning, will moderate.

The Congressional Black Caucus Institute will co-host the event. Thanks to a debate partnership with Twitter, voters will be able to tweet questions for the moderators to ask using the hashtag #DemDebate.

Ahead of the debate, ViacomCBS Newsroom spoke to Brennan about how she prepared, what she wants for the viewers, and how her previous interviews with several of the candidates on Face the Nation will inform her strategy.

What’s your focus during the debate?

Margaret Brennan: I see my role as, and this is something I think of every single week on Face the Nation, answering ‘what do people at home need to know?’ What can be a differentiating point, particularly for a candidate, from somebody else that they're standing next to on that stage and what's going to really impact [viewers]?

As moderators, it's not our job to be the center of this. In many ways, we are the people who are helping to pull information out of these candidates as they try to persuade the American people. This is part of our democracy, and I think it's a good thing to try to remember that. This isn't our television program. This is a platform for our democracy ... and it's a hugely important time in our country.

What's so interesting about the democratic candidates right now is that up until very recently, they've pretty much all just been running against Trump. I think a lot of Americans would have a hard time telling you major policy differences between them with the exception of how they want to change healthcare. The candidates haven’t had to explain themselves. I'm keenly aware of that on Face the Nation. I'll be aware of that on the debate stage too.

This will be the 10th debate in this election cycle. How do you find new questions?

MB: I've interviewed almost every single one of these candidates. I've read all their platforms, I've read all the recent press, I've read all the things they've written in major publications and journals and all the major speeches they’ve given. I soak that up and look for the top things that we as a country could have as our number one concern [to find] where they haven’t been asked to explain things before.

Also, we have this great team of embedded reporters who are contributing here, who have spent time on the campaign trail with all these candidates. We're sitting in the room and doing mock debates, so we can say this person is going to take that question and run with it in this direction, so you can anticipate where it could go next.

In the past, CBS debates have been driven by a smaller number of folks. Now that every major program on CBS News is represented on stage, there are a lot of producers working with different people in the room like Bill Whitaker and his team from 60 Minutes, as well as Major Garrett and his longtime producer. Mary Hager, executive producer of Face the Nation, along with two other really great producers from the show and my assistant are here with me.

How does the location and timing of the debate influence the questions?

MB: Norah and Gayle are driving the car on this one for the majority of the debate. They've been key in shaping all of that along with the things that are important to our co-sponsor, the Congressional Black Caucus Institute.

We try to find the unanswered questions for, in particular, the state itself. South Carolina is reflective of the rest of the country in many ways. It has a lot of diversity in its cities. It's got a lot of rural areas as well. It's got manufacturing, it's got big international corporations, and it's got small businesses. This is a really interesting state that reflects a lot of different, overlapping things.

You’ve interviewed many of the candidates on Face The Nation. Does that familiarity make you more likely to elicit clear answers? 

MB: One of the things that is different about crafting debate questions is that you don't always get the chance to ask follow-up questions like you would in an extended sit-down interview. It’s why Sunday shows like Face are so unique. I have pages and pages of questions that won't make it into this debate, but you may see them show up on Face the Nation because we are the program that will not only be covering these candidates, but speaking to them [directly] over the next nine months or so left in this campaign.

This interview has been edited and condensed for clarity. 

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The debate will air live on CBS and BET at 8 p.m. ET. Viewers can also tune into the livestream on CBSN, the network’s 24/7 streaming news service. Post-debate live coverage hosted by Elaine Quijano, anchor of CBSN's Red & Blue, and political correspondent Ed O'Keefe begins at 10:15 p.m. ET.