The 2020 election is in its early stages, but the fourth Democratic presidential debate Tuesday could shape the rest of the race for a number of candidates, including the ones leading the polls. At the end of every debate, The Fix’s Aaron Blake ranks the winners and losers from the night. Below is our analysis of what each candidate needs to do to land in the winner column.

We’ve also included their average in high-quality polls of Democratic primary voters, as compiled by The Washington Post’s polling team, and where they fall on The Fix’s rankings of who’s most likely to be the nominee.

Elizabeth Warren

Polling average: 26 percent

She has leads in some polls, nationally and in early-voting states. She is raising millions of dollars more than former vice president Joe Biden. And she’s been declared a winner by The Fix in the past three debates as other candidates have either declined to or not figured out how to attack her. But with more standing comes more scrutiny, as the senator from Massachusetts saw recently when political opponents drummed up accusations she wasn’t fired for being pregnant as a teacher. (She maintains she was.) Warren still faces questions about the financial cost of Medicare-for-all on middle-class taxpayers, as experts question her and Sen. Bernie Sanders’s assertion that costs will definitely go down. Still, with Biden focused on how to respond to President Trump and Sanders having his own problems, this is the moment Warren could stand out in a way she hasn’t yet on the debate stage: as the unequivocal leader.

Joe Biden

Polling average: 27 percent

After largely ignoring Trump’s unsubstantiated allegations that Biden as vice president intervened in Ukrainian politics to help his son’s business ties, Biden has recently switched tactics to confronting the allegations and the president. “Enough is enough,” he wrote in a Washington Post op-ed. “Trump won’t destroy me, and he won’t destroy my family.” Some of his supporters warned him that Trump and his conservative media machine will flood the information stage if he doesn’t speak up and call Trump out when he’s wrong. Biden seems to now agree. But it means he’s running an election campaign while still in a primary. And especially for that reason, his team is playing whack-a-mole with Trump allies spreading disinformation on social media and in the media. A recent poll shows a plurality of Americans are wondering if the allegations are true, and at least one of his 2020 opponents said they wouldn’t let family members have such close business ties to their work. In addition, Biden hasn’t shaken off questions about his acuity from sluggish previous debate performances. Given all this, how can Biden show Democratic voters he’s up to the task of such relentless confrontations with Trump?

Bernie Sanders

Polling average: 16 percent

The debate comes at a tough time for Sanders, who was hospitalized for a heart attack and paused campaigning, right after he shared that he raised the most money of all candidates these past three months. Sanders is 78 and the oldest candidate running for president. He would be the oldest president ever (though Biden and Warren are in their 70s, too, and would set a record if elected). His campaign waited days to announce he had a heart attack and won’t answer questions about how serious it was. The senator from Vermont is resting now and it’s possible Tuesday’s debate will be his first campaign appearance since the heart attack. It’s fair to say his age and health are the last things Sanders will want to talk about on the debate stage — but that’s reality when you’re running for president and every aspect of your life is under scrutiny.

Kamala D. Harris

Polling average: 5 percent

She had a dream first debate this summer, after attacking Biden for his position on school busing. But Sen. Kamala D. Harris failed to translate that momentum to the campaign trail. Her polling has dropped precipitously since this summer, into the single digits, according to an average of top polls from RealClearPolitics. Even her home state, California, is indifferent to her candidacy, reports The Post’s David Weigel. Harris needs an extra-strong debate performance. That will be extra tough to do on a crowded stage of 12 candidates, where the national story is elsewhere, like on impeachment.

Pete Buttigieg

Polling average: 5 percent

The South Bend, Ind., mayor continues to pull in impressive fundraising hauls — $19 million in the quarter that just ended — and has had steady debate performances. But he hasn’t dominated headlines since his entrance in the race, when some compared him to a young Barack Obama. Like Harris, his candidacy just hasn’t gained the traction he needs to reach the first tier. His biggest moments on the debate stages so far have come from criticizing Warren and Sanders’s take-it-or-leave-it liberal policy proposals, so there could be an opening there for him to be more aggressive — and more noticeable.

Cory Booker

Polling average: 1 percent

The senator from New Jersey has no problem with aggressive campaigning and debating. “Mr. Vice President, there’s a saying in my community, you’re dipping into the Kool-Aid and you don’t even know the flavor,” he said in a July debate in a back-and-forth with Biden over their criminal justice reform records. This past week, Biden has been Booker’s ticket again to national headlines. More than the other senators running, Booker leveraged his role as a senator who would be a jurist of Trump’s impeachment by defending Biden from the unsubstantiated Ukraine allegations that Trump peddled to the Ukrainian president. “... If you come after Joe Biden, you’re going to have to deal with me…,” he told CNN last week. Trump’s personal lawyer Rudolph W. Giuliani went after Booker afterward. A few days later, a fired-up Booker got a standing ovation while speaking to a receptive crowd of 300 in Iowa.

Julián Castro, Amy Klobuchar, Beto O’Rourke, Andrew Yang, Tulsi Gabbard

For these candidates, all of whom are polling at 1 or 2 percent, they need to make a moment in this debate. Controversy is always a good bet to get noticed, but there’s a way to take that overboard. (See Castro, former housing secretary, in September’s debate, who appeared to go there on Biden’s age: “Are you forgetting what you said two minutes ago?”)

The Democratic National Committee is raising the bar for who qualifies for the Nov. 20 debate, above the polling averages of a number of candidates here. Yang has made it in but the rest are in danger of not.

Tom Steyer

Polling average: 1 percent

The only new person on the debate stage Tuesday will be billionaire Tom Steyer. His campaign to date is mostly self-funded, and he entered the race late, after Biden, Warren and Sanders were already dominating the polls. Steyer is best known for his activism (and his willingness to put money behind it) on climate change and to push Democrats to impeach Trump. Now that impeachment may be happening, can Steyer have an “I told you so?” moment on the debate stage that helps place his candidacy in perspective?

Emily Guskin and Kevin Uhrmacher contributed to this report. Candidate illustrations by Ben Kirchner for The Washington Post.