LAS VEGAS — Nineteen presidential candidates made pilgrimages here Saturday, braving temperatures that exceeded 100 degrees, to show off their pro-labor credentials at a forum sponsored by the country’s largest public-sector union and pledge to elevate labor interests in their administrations.

Most were allowed only 15 minutes to speak, but the popularity of the forum underscores the importance of labor unions in the Democratic primary and showed how far candidates were willing to go to woo a key and newly energized portion of the party’s coalition.

“It’s not labor, it’s unions,” declared former vice president Joe Biden. “I can say the word ‘union’ — we don’t say it enough.”

Sen. Elizabeth Warren (D-Mass.) referenced former president Ronald Reagan’s famous line that the “most terrifying words in the English language” are, “I’m from the government and I’m here to help.”

“It is one of the most poisonous lines that’s been uttered in the last 40 years,” Warren said. “That is an attack on our government and everybody who works for our government and that is just wrong.”

The rush to stand with labor comes as many of the big unions have decided to hold off on endorsing candidates until late in the process. Some might not endorse at all. The American Federation of State, County and Municipal Employees, which hosted the forum, is no different.

“In the past, AFSCME has kind of jumped out there pretty quickly and endorsed,” said Lee Saunders, president of the union, which represents 1.4 million workers. “We’re going to slow it down this time. We’ve got a lot of friends in the race.”

During the last Democratic primary, AFSCME endorsed Hillary Clinton in October 2015, months before any of the first primary contests were held. The union waited much longer in 2008, backing Barack Obama in June of that year after most of the state primaries were complete.

The AFSCME endorsement comes with “boots on the ground,” Saunders said in an interview with The Washington Post, but he declined to say how much money the union plans to spend in 2020.

The 19 candidates were asked if they will support a bill backed by AFSCME to give government employees a federal right to organize. All said they would.

Another frequent topic was health care. The labor movement doesn’t have a unanimous view on the topic, an issue that has also divided the Democratic field.

AFSCME supports a single-payer health-care system, and union leaders said they’re telling candidates they want to be part of any discussions about changing the current system.

Warren, who supports Medicare-for-all, spoke directly to AFSCME’s desire to be part of the negotiations for a new system when she said: “As I see it, is the unions are at the table, nobody does anything without working people well represented.”

Sen. Bernie Sanders (I-Vt.) was pressed the hardest of any candidate on his health-care plan. He was asked whether he could guarantee his Medicare-for-all system would provide the same generous benefits that groups such as the Culinary Union have negotiated in their health plans.

“Absolutely. Absolutely we can,” Sanders replied.

Sen. Kamala D. Harris (D-Calif.), who initially supported a Medicare-for-all plan but recently unveiled a different plan that provides a 10-year transition to a single-payer system, said part of the reason for her shift was listening to union members’ concerns.

“That’ll allow for at least two cycles of organizing and negotiating contracts,” Harris said.

Many tried to stress that they would not take labor support for granted, a dynamic that some blame for Trump’s victory.

“A lot of labor union members drifted,” said New York Mayor Bill de Blasio. “They didn’t believe Democrats were on their side.” De Blasio said “passing the strongest pro-labor laws they’ve ever seen in their lives” would change the dynamic.

Several candidates were asked to describe how they would staff their cabinets. Sen. Cory Booker (D-N.J.) pledged to appoint someone with a background as a schoolteacher to be secretary of education. Warren has made the same promise.

Biden, asked whether he would appoint a union leader to lead the department of labor, said he would pick someone “with a heart and a head and knowledge, and that means I’ll go to the labor movement.”

He added: “I would go to people who know what it is like, what is at stake, what is needed,” adding that the person could be a labor leader, a labor lawyer or a labor professor.

When Sanders got the question, he laughed. “You have to start asking me harder questions,” he said.

“This, I do promise you,” he added. “That there will be no labor secretary stronger in the defense of the working class and trade unions than the one that I will appoint.”