It was the Detroit Donnybrook. Tuesday's Democratic debate was choppy but passionate, opening up wide philosophical divisions within the party's presidential field and providing sound bites critical of progressive ideas and candidates that Republicans are certain to use in 2020.

Moderate candidates trailing in the polls went in determined to upend Sens. Elizabeth Warren of Massachusetts and Bernie Sanders of Vermont, the two strongest candidates on the stage and leaders of the party's left. Warren and Sanders were still standing at the end. Warren was consistently crisp, displaying the mastery-on-the-run that has lifted her in the polls. Sanders pushed back again and again against rivals he cast as insufficiently open to change. But several of those running behind -- South Bend, Ind., Mayor Pete Buttigieg, Minnesota Sen. Amy Klobuchar and Montana Gov. Steve Bullock -- broke through the noise, of which there was a lot. CNN's moderators kept trying to stop candidates from speaking, and the candidates did their best to ignore them.

It gave the debate a disjointed feel, and a randomly selected group of candidates representing half the party's field created a very particular dynamic.

Before the encounter began, Democratic National Chairman Tom Perez spoke of the party having "the most diverse field in our nation's history." But all of Tuesday's candidates were white. The five candidates of color will appear in the second debate Wednesday, which will feature the other leaders in the race, former vice president Joe Biden and California Sen. Kamala Harris. They were probably smiling as they watched the first half of the field tear each other apart.

Having the two staunch progressives onstage together did not create the fight many expected: a showdown between a rising Warren and a Sanders who has been falling behind her. Instead, the two worked almost as allies in a different battle, pushing back against others who challenged progressive ideas, including a single-payer health-care system and the Green New Deal.

With former Maryland congressman John Delaney serving as a middle-of-the-road bomb thrower, attacking rivals for not understanding health care, getting their math wrong and threatening to destroy the private insurance system, Warren and Sanders got increasingly impatient. At one point, Warren turned to Delaney and said: "I don't know why anyone goes to all the trouble to run for president of the United States just to talk about what we can't do and can't fight for." Sanders expressed exasperation, as well. "I get a little bit tired of Democrats afraid of big ideas. Republicans aren't afraid of big ideas."

The debate opened with an extended scuffle about the Medicare-for-all proposal that Sanders popularized and Warren has endorsed. Supporters of the plan no doubt cheered the defenses offered by Warren and Sanders -- that it would cut paperwork, end co-pays and deductibles, take corporate profit out of the health-care equation and guarantee everyone coverage. But their foes rehearsed all the arguments Republicans will use against it, among them that it could end private health insurance (including, said Rep. Tim Ryan of Ohio, the generous plans negotiated by unions) and force large tax increases to pay for the new system.

Buttigieg and Klobuchar both defended the alternative of adding a public option to the Affordable Care Act. Buttigieg argued that if the public system worked best, Americans would flock to it and create Medicare-for-all by choice. Klobuchar spoke of the urgency of getting everyone covered and cast the public option as "the easiest way to move forward quickly."

Democrats would do well to act like a sports team, watch the film of this encounter and consider how well Medicare-for-all would hold up on the 2020 battlefield. Tuesday's test should be sobering.

As the debate wore on, many onstage seemed frustrated at the collective portrait the candidates were presenting. "We are more worried about winning an argument than winning an election," Klobuchar said. Buttigieg said that, "It's true that if we embrace a far-left agenda, they're going to say we're a bunch of crazy socialists." But the GOP would do the same, he said, if Democrats "embrace a conservative agenda." The lesson: "Stop worrying about what the Republicans will say." Author Marianne Williamson, who also had effective moments, including a moving plea for racial justice, expressed frustration with the divisive policy thicket simply: "Yada, yada, yada."

For Bullock, it was his first debate and an effective one. He stressed his successful fight in Montana against big money in politics, his success in a state carried by Donald Trump and spoke movingly of his conversion on gun control.

In the end, it was a substantive discussion, very unlike anything Trump would engage in. But it was also an evening during which Democrats watching in their living rooms confronted the possibility that the long fight between now and next summer could be irritable, difficult and fractious.

E.J. Dionne writes about politics in a twice-weekly column for The Washington Post.