Elizabeth Warren and Bernie Sanders shredded a billionaire and the billionaire class Wednesday night in the most important debate so far in the race for the 2020 Democratic presidential nomination.

With the best illustration since last summer’s Democratic debate in Detroit of how these two senators can together build a powerful case for a different kind of politics, Warren and Sanders targeted a newly arrived debater, free-spending billionaire Michael Bloomberg, while at the same time framing an argument that the Democratic Party must not barter off its future to the highest bidder.

Warren set the tone for the evening with the most powerful opening statement yet delivered in the nine debates of a Democratic race that is only now beginning to take shape. The senator from Massachusetts put Bloomberg in a box with the president Democrats are desperate to defeat in November, declaring: “I’d like to talk about who we’re running against. A billionaire who calls women ‘fat broads’ and ‘horse-faced lesbians.’ And no, I’m not talking about Donald Trump, I’m talking about Mayor Bloomberg.”

Then Warren made the political point that mattered. “Democrats are not going to win if we have a nominee who has a history of hiding his tax returns, of harassing women, and of supporting racist policies like redlining and stop-and-frisk,” she said. “Look, I’ll support whoever the Democratic nominee is, but understand this, Democrats take a huge risk if we just substitute one arrogant billionaire for another.”

Warren nailed it on a night when all the non-billionaire candidates tackled Bloomberg. And she followed up her comparison of Bloomberg’s sexism with that of Trump by deposing the Democratic billionaire regarding his use of nondisclosure agreements to hide evidence of a toxic work environment within his vast empire. This was Warren at her very best, especially when she concluded the discussion by reminding Democrats that “this is not just a question of the mayor’s character. This is also a question about electability.” She went on to explain, “We are not going to defeat Donald Trump with a man who has who knows how many nondisclosure agreements and the drip, drip, drip of stories of women saying they have been harassed and discriminated against. That’s not what we do as Democrats.”

Sanders, who has emerged as the front-runner in a race where Bloomberg is busy trying to buy his way into the top tier, made a parallel case that the richest guy ever to seek the American presidency was the wrong candidate to nominate for a November fight with the second-richest guy ever to seek the American presidency. The senator from Vermont countered Bloomberg’s “I’m the only one here I think that’s ever started a business” claptrap with a savagely on-target argument that rich guys are the problem.

Raging against “a corrupt political system bought by billionaires like Mr. Bloomberg”—and against candidates, including former South Bend mayor Pete Buttigieg, who take money from billionaires—Sanders addressed Bloomberg directly, saying, “You and your campaign contributions are electing people to represent the wealthy and the powerful.”

Sanders, whose polls put him in the lead ahead of Saturday’s caucuses in Nevada, where Bloomberg is not even competing, was anticipating competition with the billionaire in the delegate-rich Super Tuesday states that vote on March 3. After his rival bragged again about the businesses he has created, and by extension about the tens of billions of dollars he has banked, Sander shot back: “You know what, Mr. Bloomberg? It wasn’t you who made all that money. Maybe your workers played some role in that as well. And it is important that those workers are able to share the benefits also.”

Bloomberg bristled at the hits he was taking from Warren and Sanders. Asked if he would support a Sanders proposal to require large corporations to turn over 20 percent of their ownership to employees, Bloomberg growled, “Absolutely not. I can’t think of a way that would make it easier for Donald Trump to get reelected than listening to this conversation. This is ridiculous. We’re not going to throw out capitalism. We tried that. Other countries tried that. It was called communism and it just didn’t work.”

Sanders was ready for that one. “Let’s talk about democratic socialism—not communism, Mr. Bloomberg, that’s a cheap shot. Let’s talk about what goes on in countries like Denmark.… they have a much higher quality of life in many respects than we do.”

“We are living in many ways in a socialist society right now. Problem is, as Dr. Martin Luther King reminded us, we have socialism for the very rich, rugged individualism for the poor,” explained Sanders. “When Donald Trump gets $800 million in tax breaks and subsidies to build luxury condominiums, that’s socialism for the rich. Walmart, we have to subsidize Walmart’s workers who are on Medicaid and food stamps because the wealthiest family in America pays starvation wages, that’s socialism for the rich. I believe in democratic socialism for working people, not billionaires, health care for all, and educational opportunities for all.”

Sanders never let up. He pulled together objections raised by all the candidates to Bloomberg’s insensitivity when it comes to sexism, racism, and economic injustice, and said, “You know, we talk about electability, and everybody up here wants to beat Trump, and we talk about stop and frisk, and we talked about the workplace that Mayor Bloomberg has established and the problems there. But maybe we should also ask how Mayor Bloomberg in 2004 supported George W. Bush for president, put money into Republican candidates for the United States Senate, when some of us, Joe [Biden] and I and others, were fighting for Democrats to control the United States Senate. Maybe we can talk…about a billionaire saying that we should not raise the minimum wage or that we should cut Social Security, Medicare and Medicaid. If that’s a way to beat Donald Trump, wow, I would be very surprised.”

Sanders thinks he is best positioned to beat Trump. Warren begs to differ. The two candidates are well aware that they are competing with each other. They expressed differences in the debate, and they’ll continue to do so as the campaign goes forward. But on Wednesday in Las Vegas, they delivered a single message that is vital for the future of the Democratic Party.

The party of Franklin Delano Roosevelt—who in 1936 warned, “We know now that Government by organized money is just as dangerous as Government by organized mob”—cannot rent itself out to the billionaire class. That’s not just politically unwise. As Sander explained, in Wednesday night’s most unapologetically class-based appeal, “Mike Bloomberg owns more wealth than the bottom 125 million Americans. That’s wrong. That’s immoral. That should not be the case when we got a half a million people sleeping out on the streets, where we have kids who cannot afford to go to college, when we have 45 million people dealing with student debt. We have enormous problems facing this country and we cannot continue seeing a situation where in the last three years, billionaires in this country saw an $850 billion increase in their wealth. Congratulations, Mr. Bloomberg. But the average American last year saw less than a 1 percent increase in his or her income. That’s wrong.”