A total of 20 Democratic candidates will take to the debate stage in Miami this week — 10 each on Wednesday and Thursday evening.

But most of the focus will be on the top five candidates in the polls who have broken away from the rest of the pack.

ADVERTISEMENT

What does each of them need to do?

Former Vice President Joe Biden Joe BidenPelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Hillicon Valley: Subpoenas for Facebook, Google and Twitter on the cards | Wray rebuffs mail-in voting conspiracies | Reps. raise mass surveillance concerns Fox News poll: Biden ahead of Trump in Nevada, Pennsylvania and Ohio MORE

One of Biden’s most important objectives is, politically speaking, to abide by the Hippocratic oath: “First, do no harm.”

The former vice president has raised doubts about his standing as the front-runner with a couple of serious stumbles recently. If he were to misspeak or otherwise incite another controversy when he hits the debate stage on Thursday, it would be a huge problem.

Conversely, if he puts in a solid performance, that will quieten some of the concern.

Biden will almost certainly face questions about the two furors that have recently dogged his candidacy: his earlier support for the anti-abortion Hyde Amendment, which he has now reversed; and his praise for the affability of two Southern segregationists of an earlier era, the late Sens. James Eastland (D-Miss.) and Herman Talmadge (D-Ga.).

Biden faces at least two other challenges. One is whether he can counterpunch effectively if he is criticized by his rivals. It has been seven years since Biden was last in a high-profile debate — his vice presidential clash with Republican Paul Ryan Paul Davis RyanKenosha will be a good bellwether in 2020 At indoor rally, Pence says election runs through Wisconsin Juan Williams: Breaking down the debates MORE in 2012 — and the time-lag could leave him rusty.

The other task he faces is proving that he has a real vision for the nation’s future. At 76, and having been on the national political scene since the early 1970s, Biden needs to demonstrate that he is not yesterday’s man.

Sen. Elizabeth Warren Elizabeth WarrenHillicon Valley: Subpoenas for Facebook, Google and Twitter on the cards | Wray rebuffs mail-in voting conspiracies | Reps. raise mass surveillance concerns On The Money: Anxious Democrats push for vote on COVID-19 aid | Pelosi, Mnuchin ready to restart talks | Weekly jobless claims increase | Senate treads close to shutdown deadline Democratic senators ask inspector general to investigate IRS use of location tracking service MORE (D-Mass.)

Warren is the candidate with momentum, rising in the polls and — in a couple of recent national surveys — supplanting Sen. Bernie Sanders Bernie SandersThe Hill's Campaign Report: Trump faces backlash after not committing to peaceful transition of power Bernie Sanders: 'This is an election between Donald Trump and democracy' The Hill's 12:30 Report: Trump stokes fears over November election outcome MORE (I-Vt.) to take second place behind Biden.

Clearly, Warren will be hoping to keep that momentum going with a strong performance. She, famously, has specific plans for a whole host of issues. On Tuesday, she released a new one on election security.

The Massachusetts senator is in an odd spot in the debates, however. The draw to determine who would debate on which night left her the sole member of the top five debating on the first night, Wednesday.

That introduces several unpredictable dynamics.

Will Warren gain in stature because she will be the focus of attention on Wednesday, or will she be forced onto the defensive if rivals — perhaps Sen. Cory Booker Cory Anthony Booker3 reasons why Biden is misreading the politics of court packing Bipartisan praise pours in after Ginsburg's death DHS opens probe into allegations at Georgia ICE facility MORE (D-N.J.) or former Rep. Beto O’Rourke (D-Texas) — attack her, hoping to make a mark?

Similarly, she will have to judge to what extent — if at all — she should jab at top-tier rivals like Sanders and Biden, who won’t be present on the same stage and will have 24 hours to formulate a response.

The luck of the draw matters. Right now, no one knows whether it will turn out to favor or disfavor Warren.

Sen. Bernie Sanders (I-Vt.)

In polling averages, Sanders is still clinging onto second place over Warren. But his support has been basically stagnant to date and he needs to breathe new excitement into his candidacy in Miami.

Sanders is at least bringing new ideas.

On Monday, he announced a plan to eliminate all student debt — an aggregate sum currently estimated at $1.6 trillion. Sanders says this could be paid for with new taxes on Wall Street.

The proposal helps the Vermont Independent emphasize that he is to the left of Warren, his main rival for the votes of progressive Democrats. Warren proposed her own plan in April which, though ambitious, did not go nearly as far as Sanders’s.

More broadly, Sanders needs to reinvigorate his argument as to why he should be the nominee. His tendency to emphasize that he was first with ideas that other candidates have now adopted can make it seem as if he is hearkening back to 2016 rather than looking toward the future.

Sen. Kamala Harris Kamala HarrisHundreds of lawyers from nation's oldest African American sorority join effort to fight voter suppression Biden picks up endorsement from progressive climate group 350 Action 3 reasons why Biden is misreading the politics of court packing MORE (D-Calif.)

Harris, perhaps more than any other major candidate, needs some kind of big moment on Thursday.

The California senator received positive reviews for a successful campaign launch in Oakland back in January and she scores well enough in polls to be considered a top-tier candidate.

At the same time, she has remained firmly outside the top three. She has also faced criticism for cautious, fence-sitting answers. And, in a field where the other top-tier candidates can be clearly divided into progressives (Sanders and Warren) and centrists (Biden and South Bend, Ind., Mayor Pete Buttigieg Pete ButtigiegBillionaire who donated to Trump in 2016 donates to Biden The Hill's Morning Report - Sponsored by Facebook - GOP closes ranks to fill SCOTUS vacancy by November Buttigieg stands in as Pence for Harris's debate practice MORE), Harris’s ideological identity remains cloudy.

She could put that right on Thursday night. A former California attorney general and San Francisco district attorney, she is a skilled debater.

The question is whether she can provide a rationale for her candidacy that vaults her closer to the top of the field.

South Bend, Ind., Mayor Pete Buttigieg (D)

Buttigieg was an earlier flavor of the month during the media blitz that coincided with the launch of his campaign in April.

The 37-year-old mayor is an impressive television performer, which propelled him upwards in the polls — for a while.

Buttigieg, though, needs to find some way during the debates to connect with non-white voters.

His support so far depends heavily on upscale whites.

Frustrations among African Americans in his city burst into view at a Sunday town hall event after the fatal police shooting of Eric Logan, 54, a black man. Buttigieg was subject to passionate criticism, which didn’t do his presidential hopes any good.

Buttigieg needs to use all his considerable powers of communication and persuasion to steady his candidacy.