By Jonathan Martin and Alexander Burns

New York Times News Service

MIAMI — The Democratic Party’s moderate flank, led by Joe Biden, voiced disagreement and dismay in a debate Thursday about a number of left-wing policy ideas that have moved to the forefront of the party’s agenda, including proposals to create a single-payer health care system and make public colleges entirely free.

After the party’s first debate in Miami on Wednesday, an event defined largely by Sen. Elizabeth Warren’s blunt populism and ambitious policy agenda, the second forum — featuring a different set of candidates — quickly magnified the misgivings of Democrats closer to the center.

Biden, the front-runner for the Democratic nomination, avoided clashing directly with his competitors — but in a debate that was sometimes heated and often raucous, he spelled out in plain terms that he would govern as a pragmatist. Citing his modest upbringing, Biden said he would focus on providing substantial new benefits to the middle class without upending the economy.

“We’ve got to be straightforward,” Biden said, arguing for the creation of an optional government-backed health care plan but not a single-payer system. “We have to make sure we understand that to return dignity to the middle class, they have to have insurance that is covered and they can afford it.”

Two lesser-known rivals, Sen. Michael Bennet and former Gov. John Hickenlooper, both of Colorado, warned in more ominous terms about the rise of the party’s left wing, embodied by Sen. Bernie Sanders of Vermont, who joined them onstage. Hickenlooper declared that embracing socialism as a political label would lead Democrats to electoral defeat, while Bennet spoke with evident alarm about Sanders’ legislation that would void the private health insurance system.

And Mayor Pete Buttigieg of South Bend, Indiana, raised reservations about creating new universal college tuition benefits, suggesting they could end up providing unneeded financial support to wealthy students.

Yet Sanders had ample company onstage from Democrats aligned with his vision for health care and much more, including Sens. Kamala Harris of California and Kirsten Gillibrand of New York, both of whom raised their hands to endorse the replacement of private care with a “Medicare for all” system.

For his part, Sanders defended his agenda with plain enthusiasm. From his first comments of the night, he said voters were demanding “real change” from their government, and suggested without naming names that opponents like Biden were offering paltry half-measures.

Americans, Sanders said, deserved a president who would “stand up and tell the insurance companies and the drug companies that their day is gone, that health care is a human right.”

And capturing the mood of ambition among liberals, Harris — a progressive running on somewhat more traditional Democratic policies than Sanders — struck a defiant note early in the debate when moderators asked whether Democrats had a responsibility to detail how they would pay for their plans.

“Where,” Harris countered, “was that question when the Republicans and Donald Trump passed a tax bill that benefits the top 1% and the biggest corporations in this country?”

The forum grew unruly at times as many of the candidates sought to interject comments when they were not called on to speak, creating a din that eventually prompted Harris to deploy a line she plainly had at the ready. “America does not want to witness a food fight — they want to know how we’re going to put food on their table,” she said to applause.

To the surprise of no one, President Trump sneaked a look at the Democratic debate in between meetings with world leaders in Osaka, Japan. And to the surprise of exactly no one, he professed not to be impressed.

Trump evidently passed a television set just before joining Chancellor Angela Merkel of Germany. “All Democrats just raised their hands for giving millions of illegal aliens unlimited health care,” he (or perhaps an aide) quickly typed out on his Twitter account. “How about taking care of American Citizens first!? That’s the end of that race!”

He then sat with Merkel and went ahead with the same criticism of Democrats as reporters were invited in the room. “They didn’t discuss what they would do for American citizens,” he said. “That’s not a good thing.”

For the 76-year-old Biden, who leads the field in national and early-state polling, the first debate was as much about reassuring his party’s voters that he is up to the task of serving as commander-in-chief as it was about firing off a pithy one-liner or demonstrating fluency on any policy matter.