WASHINGTON (Reuters) - For most of the 2020 Democratic presidential contenders, next week’s debates will be their first leap into the high-risk, high-reward glare of the national political spotlight.

FILE PHOTO: Twenty 2020 Democratic presidential candidates who will participate in the party's first debate in Miami later this month in a combination file photos (L-R top row): U.S. Senators Bernie Sanders, Kirsten Gillibrand, Cory Booker, Kamala Harris, Amy Klobuchar, Michael Bennet, and Elizabeth Warren. (L-R middle row): Former U.S. Vice President Joe Biden, Mayor Pete Buttigieg, New York City Mayor Bill de Blasio, former HUD Secretary Julian Castro, Former Gov. John Hickenlooper, and Gov. Jay Inslee. (L-R bottom row): Entrepreneur Andrew Yang, U.S. Representatives Tim Ryan, Tulsi Gabbard, Eric Swalwell, Author Marianne Williamson, Former Representatives John Delaney and Beto O'Rourke. REUTERS/Files/File Photo

Former Vice President Joe Biden and U.S. Senator Bernie Sanders of Vermont, the race’s front-runners, are familiar faces on the presidential debate stage from their past campaigns. But the other 18 candidates who made the cut are newcomers to the experience, all striving to make a strong first impression - and avoid getting lost in the crowd.

For the top contenders, it’s a chance to build momentum. For the bottom rung, it’s a chance to break out.

“For candidates who aren’t as well known nationally, this is your shot,” said former Congressman John Delaney, who has been mired in the bottom of opinion polls despite being the first Democrat to jump into the White House race in July 2017. “This is when the bell goes off for the first round.”

Many in the national television audience of millions will be paying attention to the vast Democratic field for the first time during the two-hour debates, which will feature 10 candidates each over consecutive nights on June 26 and 27 in Miami.

Each of the Democrats vying for the right to challenge Republican President Donald Trump in November 2020 is likely to get roughly six to eight minutes to speak on the crowded stage, campaign aides say, putting a premium on the ability to quickly deliver a sharp message.

“The strategy is get your point across, never make more than one or two big points, and don’t snipe at somebody without thinking it through because you don’t want to look cranky,” said Howard Dean, a former governor of Vermont who made the leap from unknown to presidential front-runner before flaming out in 2004.

While Biden, making his third presidential bid, and Sanders, making his second, are the only contenders who have been on a presidential debate stage before, others have been tested in different political venues.

U.S. Senators Kamala Harris, Amy Klobuchar and Cory Booker participated in the high-drama confirmation hearings for Supreme Court Justice Brett Kavanaugh. Former Congressman Beto O’Rourke faced off against Republican incumbent Ted Cruz in two high-profile U.S. Senate debates in Texas last year.

Pete Buttigieg, mayor of South Bend, Indiana, took part in an eight-candidate cable television debate during his unsuccessful 2017 run for chairman of the Democratic National Committee.

GRAPHIC-Who is running in 2020? - here

‘DYNAMIC ENVIRONMENT’

But even experienced politicians can struggle to adjust to the heat of their first national White House debate.

“They will have to rehearse with 10 people. They have to understand they are going to be physically very close to each other,” said Matt Paul, a strategist who helped prepare Democratic 2016 presidential nominee Hillary Clinton’s running mate, U.S. Senator Tim Kaine, for his vice presidential debate against Republican Mike Pence.

“It’s all things that affect performance,” he added.

The number of participants has complicated the mock debates campaigns conduct as preparation, requiring nine staffers or volunteers to play the role of rivals and five more to play the debate moderators.

Delaney watched film of a 2007 Democratic debate in South Carolina that featured eight candidates, and a 2016 Republican version with 10 candidates, to get a sense of how big debates work. “You get bored with them pretty fast,” he said.

It is easy to be overprepared.

“This format benefits the improvisers, not the planners. If you have to plan for who else is there, what you are going to say, how to distinguish yourself, how to respond - that’s a lot to keep track of in a dynamic environment,” said Democratic consultant Erik Smith, who helped stage the party’s 2016 primary debates.

Political history is rife with examples of candidates who boosted or deflated their campaigns during debates. Former Texas Governor Rick Perry never recovered from his “oops” moment in a 2011 Republican presidential debate, when he painfully struggled to remember the third federal agency he wanted to eliminate.

Republican Carly Fiorina briefly caught fire after a strong performance at the first so-called “kids’ table,” second-tier debate in the 2016 race. The surge landed her on the main stage for the second debate, and her polish and willingness to take on Trump helped her poll numbers spike into double digits before she eventually ran out of steam.

Fiorina’s campaign manager, Frank Sadler, said the campaign made the decision not to overprepare her for the second debate so she could come off more authentically.

“We didn’t want her to be canned. We didn’t spend time writing lines. We didn’t spend time practicing lines,” he said. “The debates became less about policy and more about being memorable.”

Sometimes simpler is better, said Democrat Doug Hattaway, who helped debate preparations for Al Gore in 2000 and Hillary Clinton in 2008.

“It’s easy to overthink that stuff. I’ve always counseled candidates to keep their eye on the ball, which is the voter,” Hattaway said. “This is not the time to roll out your 10-point healthcare plan, you aren’t going to have time. It’s more about voters sizing you up as a leader.”