By Mark Z. Barabak

Los Angeles Times

After a two nights of debate that recast the Democratic race, a new round beginning Tuesday could shake up the contest even more by culling the presidential field to just about a handful of serious contenders.

As the candidates take the stage in Detroit, those with the most at stake are standing at opposite ends of the wide-open contest.

Joe Biden, the front-runner in polls, faces pressure to recover from a desultory performance last month in his first venture on the national debate stage since running for reelection as vice president in 2012.

Most of the rest of the candidates are desperate for a breakout moment that will lift them from the jam-packed field and build enough support for a return appearance when the debate series resumes in mid-September.

The format Tuesday and Wednesday will be familiar to any who followed the June debate. Ten contestants each night will field questions from a panel of moderators from CNN, which will carry the event nationwide beginning at 5 p.m. Pacific time. For most of the candidates the opportunity will amount to less than 15 fleeting minutes — if that — to make their best and perhaps final pitch to the largest campaign audience they may ever reach.

Once the last of the contestants clears the stage Wednesday night, the criteria to return will grow considerably stiffer and could rule out more than half of the roughly two dozen hopefuls bidding for the Democratic nomination. For many the exclusion could effectively silence their campaigns, like trees falling unheard in an empty forest.

“If they disappear after July, forget it,” said Paul Maslin, a longtime Democratic strategist who is watching the primary contest from the sideline. “They’re not in the race.”

The 20 who made the cut this round were divided through a random drawing. The most widely anticipated matchup will come once more on the second night, when Biden is set to take the stage alongside California Sen. Kamala Harris.

It was their sharp exchange over Biden’s past opposition to federally mandated school busing and his fond recollection of working with segregationist lawmakers that riveted attention, dominated news coverage and refashioned the Democratic race after the last debate.

Harris, who struggled for altitude after a strong start to her campaign, received an immediate boost from her commanding performance, which lifted her in polls and translated into a surge in contributions that reestablished her standing in Democrats’ top tier. The strong reviews more than made up for a lackluster showing in the campaign’s latest fundraising period and thus might have rescued Harris’ candidacy.

Biden’s rocky showing, in turn, raised questions of whether his status as the Democratic favorite — based in good part on his perceived electability — was deserved and whether, at age 76, he has the stamina and acuity to lead his party against President T rump.

Although Biden continues to top voter surveys, his lead has slipped. He promises a more forceful display on Wednesday night. “I’m not going to be as polite this time,” Biden told backers last week at a Detroit fundraiser.

Harris, in turn, is preparing for a more pugnacious debate as Democratic rivals, seeing her success, may seek to replicate her assertive performance and make her a target as well.

On Biden’s other side will be New Jersey Sen. Cory Booker, who is mired near the bottom in opinion surveys despite his decades-long reputation as a rising political star. He has been one of Biden’s fiercest critics, among the first to condemn his nostalgic reverie about working with racist lawmakers as well as a 1994 crime bill Biden helped pass that contributed to the mass incarceration of black and brown Americans.

Biden last week proposed steps to ameliorate some of the perceived problems with the crime bill, drawing a tart response from Booker. “You created this system,” he said on Twitter. “We’ll dismantle it.” The Biden campaign responded by highlighting a federal investigation into alleged police abuses while Booker was Newark mayor, previewing a possible flashpoint in Wednesday night’s debate.

Also onstage will be Julian Castro, the former secretary of Housing and Urban Development, who enjoyed his own fundraising spike and blip in polls after a strong June debate performance. He hopes to build on that momentum to ensure his return in September.

The random selection produced a pair of noteworthy matchups for Tuesday night as well.

The major focus will be on Sens. Bernie Sanders of Vermont and Elizabeth Warren of Massachusetts, who round out the campaign’s top tier with Biden and Harris.

The two New England friends and allies are competing for many of the same left-leaning economically populist voters, though each has been loath to criticize the other. Sanders was asked during a recent Iowa campaign swing what viewers could expect when he and Warren share the stage. “Intelligence,” he replied cheekily.

Still, the two will surely be prodded by the debate moderators to explain their differences and why each is better suited to face Trump than the other.

Another pair to watch will be two of the youngest candidates in the contest, Pete Buttigieg, the 37-year-old mayor of South Bend, Ind., and Beto O’Rourke, the 46-year-old former congressman from El Paso.

Despite their commonality as national newcomers, the two have followed distinctly different trajectories.

Buttigieg, whose youth, marriage to another man and relatively thin political resume make him an unlikely political phenom, raised the most money of any Democratic candidate in the last quarter and seems poised to campaign well into the fall.

O’Rourke, who burst into the race amid an avalanche of hype after his near-miss 2018 run for U.S. Senate, has fallen well short of advanced billing and lags far behind the front-running candidates in voter surveys.

Craig Hughes, a strategist for Colorado Sen. Michael Bennet, who is among those at risk of being shut out of future debates, cautioned against placing too much import on this round, which occurs months before any votes are cast. (Bennet will appear on stage Wednesday night.)

“It’s certainly an opportunity to make your case, but it’s not the only one,” Hughes said.

With millions expected to tune in, however, it’s not likely the candidates will get many bigger or better opportunities to make a splash while the race remains so fluid.