The biggest showdown so far in the Democratic race for president is looming.

The next debate in Houston on Sep. 12 will feature only 10 candidates — the first time that all the leading contenders will appear on the same stage.

The result will be a more dramatic dynamic than was seen in previous debates, where a larger field required holding separate events on successive nights.

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Houston will give the most serious rivals to former Vice President Joe Biden Joe BidenFormer Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick Bloomberg rolls out M ad buy to boost Biden in Florida MORE their best opportunity yet to attack him, if they wish to do so.

Biden, leading in the polls and center-stage, will be flanked by Sens. Elizabeth Warren Elizabeth WarrenOvernight Defense: Appeals court revives House lawsuit against military funding for border wall | Dems push for limits on transferring military gear to police | Lawmakers ask for IG probe into Pentagon's use of COVID-19 funds On The Money: Half of states deplete funds for Trump's 0 unemployment expansion | EU appealing ruling in Apple tax case | House Democrats include more aid for airlines in coronavirus package Warren, Khanna request IG investigation into Pentagon's use of coronavirus funds MORE (D-Mass.) and Bernie Sanders Bernie SandersSirota reacts to report of harassment, doxing by Harris supporters Republicans not immune to the malady that hobbled Democrats The Hill's Morning Report - Sponsored by Facebook - Republicans lawmakers rebuke Trump on election MORE (I-Vt.), the next highest-polling candidates.

It will be the first time Warren has debated Biden in the campaign to date.

“We’ve never seen Warren go after anyone before,” said progressive strategist Rebecca Katz. “This might be the first time she or Biden really go on offense.”

Warren has been rising in the polls and drawing large crowds to her rallies, including an estimated 15,000 people who showed up to see her in Seattle on Sunday.

But despite her strength, and that of Sanders, Biden had led almost every national poll.

The former vice president stumbled in the first debate, in Miami in late June, when he came under attack from Sen. Kamala Harris Kamala HarrisTexas Democratic official urges Biden to visit state: 'I thought he had his own plane' The Hill's Campaign Report: Biden on Trump: 'He'll leave' l GOP laywers brush off Trump's election remarks l Obama's endorsements A game theorist's advice to President Trump on filling the Supreme Court seat MORE (D-Calif.). The second time around — in Detroit last month — his performance was viewed as better but far from stellar.

Biden has been buttressed by his association with former President Obama and the staunch support he has received to date from black voters.

But he has also faced concerns about his age and sharpness after a number of verbal gaffes. On Thursday, The Washington Post reported that, on several occasions, he had garbled the details of an emotive story about meeting an American serviceman in Afghanistan.

The questions that surround Biden make the Houston debate crucial for him.

“There is the Joe Biden who shows up in polls and there is the Joe Biden who shows up on the debate stage, and so far those have been two different men,” said Jehmu Greene, who was a candidate to chair the Democratic National Committee in 2017. “Voters want to see the Joe Biden who can beat Trump, and we have not seen that person on the debate stage.”

But some Democratic strategists say there is an upside as well as a downside for the former vice president, if he can deliver a strong enough performance to quieten anxiety.

“The biggest risk is to Biden, because mistakes in debates generally have more impact than solid performances,” said Democratic strategist Steve McMahon. “But, by the same token, the people who love Joe Biden but have been wondering about him can be reassured by a good performance. The vice president has a lot to lose but a lot to gain, potentially, as well.”

There is also the question of how aggressive Warren and Sanders will be — with each other, as well as with Biden.

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The two senators are battling for progressive votes, hoping to become the left-leaning alternative to the more centrist Biden. But when Warren and Sanders appeared on the same debate stage in Detroit, there was little sharpness to their exchanges. Instead, they formed a relatively united front against attacks from more moderate figures.

Sanders and Warren are said to be personally fond of each other, and their common ground on policy could help them transcend their rivalry for now, even if the comity doesn’t last.

“September seems real early for them to start putting the gloves on and going after each other,” said Democratic pollster and strategist Paul Maslin. “It seems more likely to me that they will view [the debate] as a way to garnish their progressive credentials and see if they can exploit Biden’s weaknesses.”

Maslin also noted that the visuals of the debate could be as important as anything else. The image of Biden, Warren and Sanders in the middle of the stage could further crystallize the idea that they are the big three in the race — and make it harder for other candidates who are receiving measurable levels of support to make a real impact.

“If Warren and Sanders choose to put pressure on Biden, will that be the dynamic that dominates the debate? Then Harris and [South Bend, Ind., Mayor Pete] Buttigieg and everyone else will be just trying to be noticed,” Maslin said.

Harris got a sizable boost in the polls in the wake of the first debates in Miami. Her critique of Biden for his opposition to federally mandated school busing, and for his warm words about segregationist senators, dominated media coverage on the night and afterward.

But Harris’s poll ratings have faded, and she faces continuing questions about her core beliefs. She may need another standout performance to revive her candidacy.

There is another story about the Houston debates, too: that of the candidates who did not make it.

Sen. Kirsten Gillibrand Kirsten GillibrandSunday shows preview: Justice Ginsburg dies, sparking partisan battle over vacancy before election Suburban moms are going to decide the 2020 election Jon Stewart urges Congress to help veterans exposed to burn pits MORE (D-N.Y.) quit the race almost as soon as her failure to qualify became apparent. Sizable names in national politics, including Rep. Tulsi Gabbard Tulsi GabbardRepublicans call on DOJ to investigate Netflix over 'Cuties' film Hispanic Caucus campaign arm endorses slate of non-Hispanic candidates Gabbard says she 'was not invited to participate in any way' in Democratic convention MORE (Hawaii), New York City Mayor Bill de Blasio Bill de BlasioOVERNIGHT ENERGY: California seeks to sell only electric cars by 2035 | EPA threatens to close New York City office after Trump threats to 'anarchist' cities | House energy package sparks criticism from left and right EPA threatens to close New York City office after Trump threats to 'anarchist' cities New Year's Eve in Times Square to be largely virtual amid pandemic MORE and Sen. Michael Bennett (Colo.) were among the Democrats who did not make the cut.

The road ahead for them looks bleak.

Even for the leading candidates, there is no room for error in Houston.

“The stakes are much higher — and mistakes will have a significant greater impact,” said Greene.

The Memo is a reported column by Niall Stanage, primarily focused on Donald Trump’s presidency.