The top tier of the 2020 presidential race is incredibly fluid, and Wednesday night’s Democratic debate likely won’t change things much.

The four-person top tier of a large presidential field has been set for the past month: Former Vice President Joe Biden, Sens. Elizabeth Warren and Bernie Sanders, and South Bend, Indiana, Mayor Pete Buttigieg. But in this tier, there’s no one in a clear position to snag the nomination — and there hasn’t been for a while, especially in key early states.

“I haven’t seen a leader statistically in really any of the polls,” University of New Hampshire political science professor and pollster Andy Smith told Vox. “There are a lot of candidates, there’s no identified frontrunner.”

During the debate, each of these candidates answered questions playing to their strengths; Warren landed a punch with an exchange on her wealth tax, Biden talked about foreign policy and the lack of civility in America, Sanders touched on his signature issue of Medicare-for-all, and Buttigieg took time to pitch himself a moderate alternative to the left wing of the Democratic Party.

Buttigieg, who has seen a recent surge in Iowa and New Hampshire polls, faced more attacks than his counterparts. It was a scene reminiscent of the October debate, which saw Buttigieg himself attacking Warren on her pitch for Medicare-for-all.

But the fundamental dynamic characterizing each debate so far did not change; the stage was incredibly crowded, leading to rushed responses. The top four candidates were drowned out by others; for instance, questions on climate change went to billionaire Tom Steyer and Rep. Tulsi Gabbard.

Wednesday night featured few fireworks between the frontrunners themselves (although Biden and Buttigieg each had to navigate tough questions about their records on race and drug policy).

The night gave all four frontrunners some wins, and a few losses. Still, not much happened to dramatically reshape the state of the race.

The fluid state of the top tier, explained

There hasn’t been a clear frontrunner in the 2020 race for over a month, as Biden’s early lead has diminished somewhat nationally and by even more in the key early states of Iowa and New Hampshire.

Pollsters and political experts in all four early states told Vox they see the race at the top as constantly shifting. Buttigieg is now leading in Iowa, and Warren and Biden are leading in New Hampshire. Sanders has also strengthened his position after recovering from a heart attack, and he is a formidable candidate in part because he’s popular with young and working class voters, and his supporters are so loyal.

Although Biden is doing the strongest among black voters in South Carolina, political experts in that state said things could also change. And of course, there are over 10 other candidates waiting for their chance to vault to frontrunner status.

“Biden, of course, is the person that everybody’s expecting to do well, and he has a good local ground team who’s doing a lot of stuff,” said Anton Gunn, Obama’s 2008 South Carolina political director, who is not affiliated with any current campaign. “But the support for him is soft, which is not hard yes’s for Biden. [It’s] movable.”

Veteran Iowa pollster Ann Selzer told Vox that the fluidity of the top tier could reflect general election anxiety, and voters’ continued fears that much of the top tier cannot beat President Donald Trump. That’s also leading to the continued entrances of new candidates into an already huge field, like former Massachusetts Gov. Deval Patrick.

“There’s a skittishness about the chances of these top four candidates,” Selzer told Vox. In a recent Des Moines Register/CNN poll of Iowa she conducted, Selzer asked likely Democratic caucus-goers how confident they were about the chances of each of the four candidates beating Trump. Biden was the only one who got a majority, and even that was a slim majority of 52 percent. Warren and Buttigieg each got 46 percent of voters who thought they could beat Trump, while Sanders got 40 percent.

While Biden is still hanging onto a solid lead in South Carolina, the race is also fluid in New Hampshire and Nevada. Political experts in the latter two states told Vox they’re looking at the in-state infrastructure the campaigns are building, instead of at polls.

Building momentum is an important part of running a presidential campaign. But so is building a campaign infrastructure in all four early states.

New Hampshire voters have a reputation for tuning in to the election later than Iowa caucus-goers, making building an organization to capitalize on Iowa momentum key. UNH pollster Smith noted Warren’s campaign has been building formidable infrastructure in New Hampshire, as well as Sanders and Buttigieg. Strong organizing is also key to win Nevada and South Carolina, the diverse third and fourth early state to vote.

“I’m more interested in who is really staffing up, understands the state — who can capitalize on what happens in Iowa and New Hampshire,” said Nevada Independent editor Jon Ralston, the dean of the state’s political press corps.