We’re about nine months into the Democratic presidential primary race and a fair question is: Do we know more today about who is going to be the Democratic nominee than we did in January?

When Joe Biden announced he was running for president at the end of April, he was averaging about 30% support in national Democratic primary polls, just as he had been at the start of the year. Today — after some spring and summer spikes and drops — Joe Biden is...averaging about 30% in Democratic primary polls. That places him now, on average, ahead by about 11%. Early state polls have moved more, but in most, Biden’s still leading.

Biden — after months of concern (public and private) about his age, fit in the current Democratic Party, relative moderation, tendency to say things he didn’t mean to say, and focused attacks from his competitors — is still the apparent frontrunner.

Tonight will be the most meaningful test yet of how lasting that will be.

This will be the first debate with all of the leading Democratic candidates on one stage. And, probably most compellingly, it’ll be the first time Biden will debate Elizabeth Warren.

As she’s moved up into a competitive second place with Bernie Sanders, Warren has had a weird debate ride. In June, she shared the stage with people polling well below her, and largely stayed in the background. Her second debate, in July, was a kind of absurdist tag-team match: Moderators pitted Warren and Sanders against a rotation of people who probably won’t be president (one of them, John Hickenlooper, has already dropped out).

So in a real way, this is Warren’s first serious debate. It’s her first with Biden, first with Kamala Harris — who has proven she’s willing to take on leading candidates and can command a stage. She’s been onstage with Pete Buttigieg before, but post-hype, building-up Buttigieg is a little different than the version that was around over the summer dealing with crises back home.

And it’s not like Warren and Biden don’t have anything to talk about. Biden in the last few days has talked about how “we need more than plans”; Warren is the physical embodiment of “plans.” Biden’s candidacy is in part riding on the belief that people will want to look backward to Barack Obama and to a fantastical time of bipartisan camaraderie; Warren’s candidacy is riding on the idea of “big structural change.” Biden is the candidate whose wife recently told voters “you may like another candidate better but you have to look at who’s going to win”; Warren is the candidate trying to convince voters that what they think about “electability” is wrong.

All of this should be compelling to watch. And, unlike much of the last two debates, it should actually tell us something new.

It’s been genuinely hard to learn much of anything in the debates so far. For one, there have been too many people. And the things candidates have argued about in their 30-second bursts of speaking time have been confusing and sort of meta — the last debate featured what felt like hours of arguments about health care plans that were nearly impossible to follow if you weren’t already very familiar with the candidates’ health care plans (they were also very hard to follow if you were familiar). A debate with 10 candidates (or, really, 20 divided across two nights) is a pretty terrible format for getting any sort of understanding about what candidates actually want to do as president and how they want to do it. Sure, Cory Booker had issues with Biden’s history on criminal justice; a whole host of people who won’t be onstage tonight had issues with Sanders’ Medicare for All plan; Marianne Williamson had a unique interest in New Zealand’s children. But the depth that could make these moments feel more lasting than a tweet just hasn’t been there — just see how quickly Harris’s polling spike evaporated after the first debate when she took on Biden over busing.

But when you get a chance to see the top 10 candidates all in one place, you can get a real sense for who is actually good at running for president — who is able to give clear and concise reasoning for why they should be president, who is able to give answers to questions that don’t feel listless or insincere, who is able to find emotion in an overly formalized ritual, and who is able to hold their own against attacks on their records and visions.

If you’re looking to learn a lot about the candidates’ policy ideas, or to hear them go deep on what they’d want to do as president, this probably isn’t the format you’re looking for (town halls can be much better for that). But if you want to see who these candidates are under pressure, how they contrast themselves with one another personally and in terms of their broad goals, you should definitely watch tonight’s debate. Altogether, what happens could begin to answer the question of whether or not Biden’s lead really is fragile, and what it would take for his stable polling numbers to get shaky.

Also, Beto O’Rourke might say “fuck” on national TV.