"The most important question that the candidates have to answer, and answer persuasively, is why they are the strongest choice for defeating Donald Trump," Melissa Michelson, PhD, a Menlo College professor of political science, tells Bustle. "I have yet to hear most of them give an answer that is compelling in terms of why the best way to fight back against Trump is for them to personally run for president."

Beating President Trump, of course, is the ultimate goal for all of these candidates — but there's also the question of how.

"The candidates need to have a good answer about how they are going to be able to fire up the Democratic electorate," Michelson says, noting that Hillary Clinton lost in part because of low enthusiasm and turnout. The Democrats reclaimed the House in the 2018 midterms by harnessing both of those forces.

The real work of governing starts after you've won the race to the top, of course, and the candidates will need to address that in the debates.

"It's fine to say that you support the Green New Deal or immigration reform or common sense gun law reform, but presidents need to work with Congress," Lisa Burns, PhD, professor of media studies at Quinnipiac University, tells Bustle. "So, how would they, as a Democratic president, work across the aisle to garner support from Republicans?"

Michelson, however, believes that the current situation in Congress makes the promise of bipartisanship a "pie-in-the-sky."

"How will these Democrats actually make things happen? Will they rely on executive orders? Will they push to eliminate the filibuster?" she asks. The candidates need to give "honest answers about the degree to which they are willing to challenge norms or use unilateral executive power to achieve their campaign promises."

Burns says that many 2016 Republican primary campaigns met their demises because those candidates turned the discussion onto Trump's potential drawbacks rather than focusing on their own qualifications. Democrats this year will have to avoid doing something similar.

"I would like to see them answer this question by talking about their own records and ambition instead of describing themselves in contrast to the other Democratic candidates or to President Trump," Burns says. "If a candidate can provide a memorable answer to this question that inspires a voter to simply consider supporting them at this early stage, they can consider it a win."

Yes, all 45 presidents so far have been men. Almost all of them have been Protestant Christians, all but one of them has been white, and none has openly been a member of the LGBTQ community. Nowadays, though, the Democratic electorate looks different.

"It will be particularly important for all candidates, and specifically white men, to both consider and demonstrate how they will bring diverse voices, perspectives, and experiences to the table in their administrations," says Kelly Dittmar, PhD, an assistant professor of political science at Rutgers University–Camden and scholar for the Center for American Women and Politics. "Candidates should be thinking about both the advantages and limitations of their own lived experiences in shaping their policy priorities and perspectives."

Stuckey thinks that this could be a big problem for two of the frontrunners. "Sanders has the same problems as Biden in that they are older and white, and in many ways don't seem to get current conversations about race gender, and social justice," she says. "They tend to be a bit tin-eared on those issues, and that could be on display to their detriment."

And as Acker-Lyons tells Bustle, this all has to do with the moment that the country is in right now — a moment when previously marginalized groups are taking more and more control in the Democratic Party.

"The fundamental question is, why you, why now," Acker-Lyons says. "Not only why you want to be president, but why are you the right person to be president in this moment."

The Democratic Party is wrestling with what it means to be progressive — and whether that's actually a desirable adjective for a prospective candidate.

"It's become quite the buzzword," Burns says. But when Joe Biden defines himself as progressive, and other candidates "conflate 'progressive' with socialist,'" as Burns puts it, there's definitely some confusion on the topic.

"[The Democratic Party] would benefit from some clarity on this topic going into the primaries," Burns says.

Tammy Vigil, PhD, associate professor of communication studies at Boston University, notes that there's a fine line to walk here.

"To win the party's support, a more liberal lean is often key, yet to win the White House a more moderate perspective is usually necessary," Vigil says. "How candidates thread this needle will be interesting to watch and could thin out the vast pool pretty quickly when voters really start paying close attention."

Aimee Allison, the founder of She The People, tells Bustle that speaking to women of color is a key piece of any potential Democratic candidate's ability to get elected. She The People has found policies surrounding racial, gender, and economic justice to be central to women of color's decisions, so candidates will need to address them well.

"If you don’t embrace these issues of justice in 2019, you’re not going to motivate and build a multi-racial coalition that will win," Allison explains.

After all, she says, President Barack Obama got elected because he was able to motivate a diverse coalition of voters, including people of color.

"Not only is it that women of color are shaping this primary, but it is our votes that are going to ultimately determine who’s actually electable to win the white house in 2020," Allison says.

You won't hear this question coming from NBC's moderators, but as Stuckey says, the substance of the debate may not end up being that important.

"As always in a debate, it's equal parts policy and performance; and those parts probably aren't actually equal," Stuckey said. "Many people won't watch; media frames matter. And frankly, media frames for elections are bad. The horse race coverage, obsession with personality, and the way the media treat women is terrible."

If you do want to believe that the candidates' individual answers will matter, though, then Burns nicely sums up the central dilemma facing each of the candidates before the debate.

"Ultimately, the candidates are going to have very little time to say anything of substance given that there will be 10 people on stage and only two hours for the debate," she says. "So, they need to make every comment count."