Democratic presidential contenders Sen. Bernie Sanders of Vermont and Sen. Amy Klobuchar of Minnesota headlined the International Association of Machinists and Aerospace Workers (IAM) Transportation Conference in Las Vegas on Monday, giving dueling speeches that leaned heavily on their connections to organized labor.

The visits, Sanders’ second and Klobuchar’s first as candidates for the Democratic presidential nomination in 2020, come as each looks to solidify a presence among union Democrats. The cohort of voters is an increasingly small portion of the overall Democratic base as unions shrink but remains a powerful force in enclaves such as Las Vegas.

“What the billionaire class understands is that if they can destroy organized labor, if they can destroy the ability of workers to engage in collective bargaining and earn decent wages and decent benefits, if they destroy the ability of working people to come together and fight politically for a Congress that represents them and not just the wealthy — if they can do all that, who in America is left to stop their greed. The answer is: nobody is,” Sanders said.

To a standing ovation, Sanders told the crowd — roughly 800 IAM members filling a ballroom inside the Paris Las Vegas — that unions were “the last line of defense for the working families of this country.”

Sanders and Klobuchar pitched their campaigns to the audience in wide-ranging addresses that looked to pump up the union crowd on issues such as trade, infrastructure and economic inequality.

Those issues have been a bedrock for Sanders on the national stage since 2016, when the self-described Democratic socialist campaigned hard on economic issues and railed against what he’s described as abuses of the system by billionaires and corporate interests.

“Corporate America and the billionaire class have been waging a forty year war against the trade union movement in America,” Sanders said. “When Donald Trump appoints some of the most anti-union members to the National Labor Relations Board, make no mistake about it. He is waging a war against workers.”

Sanders, who lost the Democratic contest in 2016 to Hillary Clinton, entered the race earlier this year as a leading candidate, trailing only former Vice President Joe Biden in some early primary polls. The Vermont senator’s momentum continued into April, when he posted fundraising totals of more than $18.2 million — more than any other Democrat in an increasingly crowded field.

Klobuchar’s entrance into the race was less smooth, marked by a report involving her treatment of congressional aides in the workplace. Even so, the Minnesota Democrat has since mounted a campaign as a noted centrist in a field of progressives, looking to lean on her midwestern credentials in a new crop of swing states across the rust belt in the Midwest and Northeast.

“I stand before you today as a granddaughter of a union-member iron ore miner, as the daughter of a union-member newspaper man, and a daughter of union-member teacher and the first woman elected to the United States Senate from the state of Minnesota and a candidate for the president of the United States. That is what unions are about,” she said.

In Las Vegas, she stuck to that message, touting a platform centered on infrastructure investment and renewed enforcement of antitrust laws.

“Well guess what? We are now in our new Gilded Age,” Klobuchar said. “The companies are different, but it's the same kind of thing that's happening right now where workers’ power gets lessened, and wages can go down when you don't have enough competition.”

Klobuchar’s appearance was part of a series of weekend stops in Las Vegas, where she also hosted a meet-and-greet Sunday night and made a speech on school infrastructure at J. Harold Brinley Middle School on Monday morning.

Klobuchar’s visit to Brinley Middle School follows the release late last month of her infrastructure plan that includes an education component. The Las Vegas school she toured Monday is 50 years old and subject to faulty air conditioning and plumbing systems. Maintenance backlogs are a persistent problem within the Clark County School District.

“What happens is we kind of wait for things to fail or break,” Principal Brett Booth told her.

The Minnesota senator said a situation in Baltimore last year — when students wore winter coats inside classrooms because of heating problems — prompted her to include schools in her infrastructure plan. The proposal would spend $1 trillion in federal funds upgrading a variety of things in the nation’s infrastructure, including rail lines, roads, bridges and broadband internet, among other needs.

“We should include schools and these kind of less glamorous projects like heating and air conditioning,” Klobuchar said.

The presidential hopeful touted her infrastructure plan as something that ultimately could put more money in the pockets of Nevada schools. She said it would be a separate funding stream.

“Then the state can focus more on the per-pupil (funding) and some of these other things,” she said. “I don’t see it as either or. I see it as helping supplement from the federal government.”

While touring odd-shaped classrooms in Brinley Middle School, which has a circular layout, Klobuchar shared anecdotes about how her mother taught second grade until she was 70 years old and how her daughter attended public schools alongside many Somali refugees.

She called education the great equalizer and vowed that her infrastructure plan would prioritize the students and areas most in need.

Klobuchar also touched on the overall unrest the nation has seen among teachers in the last year or so. Educators went on strike in several states, arguing for a combination of better pay, increased school funding and, in the broadest sense, more respect.

“I think we need to elevate educators in how we talk about them,” she said. “A lot of what’s going on right now is all the bashing of public schools. The more that we can elevate those teachers and explain what they do — the ones I met here today — I think that’s important. The second, of course, is increasing teacher pay. That would be part of my work as the kid of a teacher.”

Klobuchar said the federal government can help provide funding for increasing teacher pay.

As her Las Vegas visit wrapped up Monday morning, Klobuchar also addressed a very Nevada issue — Yucca Mountain and the controversial secret shipment of plutonium that occurred last year.

Klobuchar said she supports “consent-based decisions” regarding the storage of nuclear waste and condemned the plutonium incident.

“That was outrageous,” she said. “What are we like back in, like, the early days of Siberia or something? That is the exact kind of thing that causes distrust in our government, and the administration should never have let that happen.”

The pair are just the latest visitors amid a flurry of presidential activity in the Silver State. Elizabeth Warren and Donald Trump headlined events over the weekend, while South Bend, Indiana Mayor Pete Buttigieg also made stops in Las Vegas on Monday.

For a full log of every presidential election visit, including who visited, where and when, check our 2020 Presidential Candidate Tracker.

This story has been updated to include material from Klobuchar's second stop in Las Vegas on Monday morning.