Thousands of pounds of fish, thousands of voters and 21 presidential candidates: What to know about Rep. Jim Clyburn's 'World Famous Fish Fry'

COLUMBIA, S.C. -- South Carolina played host to 4,400 pounds of fish, 6,400 slices of white bread and a lot of cringeworthy punchlines Friday night.

Just as the food supplies ran out -- 21 Democratic presidential hopefuls took the stage to each make a brief pitch to thousands of voters at Rep. Jim Clyburn's annual "World Famous Fish Fry" in Columbia, South Carolina, ahead of the South Carolina Democratic Party Convention on Saturday.

Former Vice President Joe Biden, who boasts a close friendship with Clyburn as a veteran third-time fish fry attendee, focused on delivering one concise message in his short speech: "Whomever the Democratic nominee is, we have to stay together and elect a Democratic president of the United States of America."

Sen. Cory Booker, of New Jersey, who was seen hugging Biden off-stage after a week of animosity between the two over comments on segregation, followed Biden in emphasizing the importance of unity in the party.

"This election is not about one person and one office, it is about who we are as a nation and who we must be to each other," Booker said. "We all must make sure that we may be in the midst of a primary, but when the primary is over, we become a united force. Not just to beat one guy in one office, but we become a united force to put the indivisible back in this one nation under God and stand up for liberty and justice for all."

Booker closed his remarks with a joke for the fish fry: "Let’s not flounder, let’s get out there and kick some bass."

Many others, including former Rep. Beto O'Rourke, of Texas, Sens. Elizabeth Warren, of Massachusetts, and Any Klochuchar, of Minnesota, addressed some of the big issues the country is facing, such as health care, public schools, criminal justice reform and climate change.

"We make this government work for us, and that means we’re just getting started," Warren said. "We need to attack our problems head on. We need to attack climate change head on. We need to attack the control of the NRA head on. We need to have courage in this country. So for me, it’s about building a future. This is our chance. 2020. We can dream big, fight hard, and win!"

Sen. Bernie Sanders, I-Vt., the only one in his button-down while all 20 other candidates were wearing matching Clyburn T-shirts, emphasized the power of unity in defeating the current president.

"Brothers and sisters, at the end of the day, the 1 percent, they got a lot of money and they got a lot of power," Sanders said. "But we got something they don't have. We are the 99%. And 99%, is a hell of a bigger number than 1%. Let us stand together. Let us defeat Trump. Let us transform this country."

Sen. Michael Bennet, of Colorado, one of the lesser known candidates, drew laughs from the audience by taking a jab at President Donald Trump.

"In my view, we have a president who doesn’t care about America," Bennet said. "I don’t think he loves America. I don’t think he loves anybody but himself."

Sen. Kamala Harris, of California took a more serious tone, reminding the crowd of the South Carolina mass shooting that killed nine people at Mother Emanuel AME Church four years ago.

"And in this fight, this is a fight not only to recognize our history and honor the ancestors and honor the heroes," Harris said, "it is a fight for our future, and a vision of our future."

The largest gathering so far for the 2020 contenders -- and a prelude to the first Democratic debates next week -- ended with remarks from Rep. Tulsi Gabbard, of Hawaii, followed by a group photo with all the candidates on stage.

Since its inception, the fish fry, which is free and open to the public, has been an effort to give South Carolinians a glimpse at candidates without the cost of attending the South Carolina Democratic Party Convention's Blue Palmetto Dinner. Tickets to the sold-out dinner cost $150.

The fish fry isn't only about making a good impression on voters, it's also about forming key relationships with the Democratic establishment in South Carolina.

Clyburn, the third-highest-ranking Democrat in the House of Representatives, has hosted the fish fry for nearly three decades. He's considered the most influential leader in South Carolina politics and his endorsement is highly coveted.

Though Clyburn has promised to refrain from endorsing a candidate ahead of the state's Democratic primary in February, in 2016, Clyburn endorsed former Secretary of State Hillary Clinton after saying he would stay neutral. He didn't publicly endorse a candidate during the 2008 Democratic primary.

"Vice President Biden has the inside track because of his name I.D., because of his established relationships with the state," Harrison said. "Many of these presidential candidates are new to South Carolinians and to the South Carolina Democrats."

Still, other 2020 presidential hopefuls are hoping to make inroads in South Carolina -- a state where African-Americans make up nearly 30% of the population.

BothBooker and Harris have campaigned heavily in the state, venturing out of the two large metropolitan areas, Charleston and Columbia. While others, like South Bend, Indiana, Mayor Pete Buttigieg, have struggled to garner much African American support at events in the state.

Buttigieg skipped the fish fry to hold community meetings following the fatal shooting of Eric Logan, a black man, by a white police officer in his hometown.

The mayor, who traveled back to South Bend after his remarks earlier in the day at the National Association of Latino Elected and Appointed Officials (NALEO) in Miami, was surrounded by members of the community and activists, including individuals holding Black Lives Matter signs, who jeered and heckled the candidate.

Jaime Harrison, a former chair of the South Carolina Democratic Party and current U.S. Senate candidate, recommended that candidates shore up their South Carolina teams with staffers that have strong ties in the state. He says doing outreach in some of the most rural corners of South Carolina is critical.

"Speak with Democrats that not only live in urban areas, where most of the state's population is, but also in many of the rural communities which will probably be very influential in determining who ultimately wins the primary," Harrison said.

ABC News' Johnny Verhovek, Briana Stewart, Beatrice Peterson and Soorin Kimcontributed to this report.