Sanders and Warren, the two-highest polling candidates on the stage in Detroit, became the main targets of several candidates who have struggled to win support. They were forced to fend off attacks by other Democrats like former Maryland Congressman John Delaney, who asserted that Democrats will win with “things that are workable, not fairy tale economics.”

Warren shot back, “I don’t understand why anybody goes to all the trouble of running for president of the United States just to talk about what we really can’t do and shouldn’t fight for. I don’t get it.”

The lively debate showed the central tension in the Democratic nomination race between the party’s liberal faction and centrists over the best path to beating President Donald Trump next year. The Democrats’ key to capturing the White House is winning back some of the working-class voters who backed Trump in 2016.

Warren said the time for half-measures has passed. On health care, for instance, the U.S. has already tried a system of Medicare, Medicaid and private insurance that hasn’t worked.

Sanders said the path to beating Trump would be difficult and “we need to have a campaign of energy, excitement and of vision” to get there, which includes motivating younger voters with promises he’s made, such as free college and student debt forgiveness.

Former Colorado Governor John Hickenlooper was presented with an advertisement in which he warned that Sanders’s embrace of socialism was too extreme to win against Trump. Medicare for All and the Green New Deal amount to “a disaster at the ballot box,” he said. “You might as well FedEx the election to Donald Trump.”

Sanders noted that he leads Trump in some polls of hypothetical general election matchups. “The reason we are going to defeat Trump and beat him badly is that he is a fraud and a phony, and we’re going to expose him for what he is,” he said, listing his efforts to raise the minimum wage and cut prescription drug prices.

The candidates clashed sharply over their health-care plans and immigration, two major issues for Democratic voters.

Warren and Sanders were the target of opponents who warned about raising taxes on the middle class and reversing the gains of the Affordable Care Act if the Medicare for all plan they both support were enacted.

“We have tried this experiment with the insurance companies and what they’ve done is they’ve sucked billions of dollars out of our health care system and they force people to have to fight to try to get the health care coverage that their doctors and nurses say they need,” Warren said.

Hickenlooper, one of a handful of candidates who favors a public option while continuing to maintain the private insurance system, said he could see Medicare for All becoming a reality in time, but that the way to get there would be through “an evolution, not a revolution.”

Ohio Representative Tim Ryan warned that Medicare for All could hurt union members who had negotiated for generous health insurance programs, but Sanders insisted that his plan “would be better” and would include hearing aids and eyeglasses.

“You don’t know that, Bernie,” Ryan interjected. “I do know that,” Sanders shot back, “I wrote the damn bill.”

Delaney’s description on Medicare for All as bad policy and bad politics, Sanders told him “You’re wrong.” Delaney retorted that “my colleagues don’t understand the business” of private health insurance.

The candidates took a firmer tone on illegal border crossings, with most saying they would continue to criminally prosecute those who jump egregious cases of border-crossing while ending policies that rip immigrant families apart.

“Right now, if you want to come into the country, you should at least ring the doorbell,” Ryan said. “It’s a shame what’s happening, but Donald Trump is doing it. So we’ve got to get rid of Donald Trump.”

Former Housing Secretary Julian Castro’s proposal to shift immigration enforcement from criminal to civil penalties pulled the Democratic field to the left in the first debate in June. But a month later, candidates like Pete Buttigieg and Beto O’Rourke clarified that civil penalties were part of comprehensive reform and criminal laws would still be used for the worst offenders.

But Sanders remained committed to decriminalizing border crossings — and to providing health insurance to those who do.

“What Trump is doing though his racism and xenophobia is demonizing a group of people. And when I’m president I will end that demonization,” he said. ”I talk about health care as a human right, and that applies to all people in this country. And in a Medicare for All system we can afford to do that.”

Warren also said she would wouldn’t charge border crossings criminally, leading Bullock to shoot back, “You’re playing into Trump’s hands.”

Warren and Sanders are competing for leadership of the Democratic Party’s progressive wing and trying to dislodge former Vice President Joe Biden as the front-runner.

Throughout the campaign, Sanders and Warren have kept to a virtual non-aggression pact, agreeing on many key issues in the race. Both are polling at about 15% nationally, but Warren has been rising mostly at the expense of Sanders. To overtake Biden, they’ll need to distinguish themselves from each other without alienating the party’s left flank.

Sanders and Warren, who want to take on corporations and Wall Street, are facing several of the party’s more pro-business moderates, all of whom have been trailing well behind the Biden, Sanders, Warren and Kamala Harris.

That leaves O’Rourke and Buttigieg some where in limbo — with enough support to make the next round but vying for support for their more traditional form of liberalism.

Bullock was making his first appearance on stage, replacing Eric Swalwell, who dropped out shortly after the last debates. More campaigns may fall by the wayside after the debate.

Sanders narrowly beat Hillary Clinton in Michigan’s 2016 Democratic primary. In the general election, Trump won the state by 10,704 votes, the first time a Republican candidate won Michigan in 28 years.

The state’s workforce is 15% unionized, and Democrats are hoping to win back the blue-collar workers who voted for Trump in 2016.

“We’ll be listening for a candidate who will use the presidency to make our country work for working people, a candidate who will defend and strengthen our right to join a union, a candidate who will finally bring the era of corporate government to an end,“ said AFL-CIO President Richard Trumka, warming up the audience at the Fox Theater before the debate. “We’re not settling for anything less.”

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