Bernie Sanders was at it again — center stage, his baritone building to something — right hand raised and restless, as if he were scribbling his words on an invisible chalkboard.

“Medicare for All is comprehensive,” he insisted, swatting away concerns that his health care plan might imperil benefits for union members. “It covers all health care needs,” he said.

Older Americans, he enthused, would be covered for dental care, hearing aids, eyeglasses.

“You don’t know that,” Rep. Tim Ryan, a union-country congressman from northeast Ohio, interjected, later reasoning that Sanders “does not know all of the union contracts in the United States.” “You don’t know that, Bernie.”

Ryan turned to face him. For a moment, Sanders appeared inclined to ignore the interruption.

“Second of all, second of all,” he said, waving off Ryan.

Then the Vermont senator reconsidered.

“I do know it,” he said. “I wrote the damn bill!”

For months, Sanders, 77 and familiar by now, has often strained to stand out in an oversize field stocked with fresher faces. He has appealed to voters’ memories of his insurgent challenge to Hillary Clinton in 2016, barely changing his stump speech for the 2020 race. He has reminded audiences that he was at the leading edge of the Democrats’ leftward lurch: free college, Medicare for All, higher taxes on the wealthy. And while few can summon the rumpled zeal of Sanders in full riff, some in the party have appeared to view Sanders as a less essential vessel, welcoming a new voice if it sounds enough like his.

But in his blithe dismissal of Ryan on Tuesday and other exchanges like it — with several candidates nipping at him and a team of CNN moderators goading the contenders into open conflict — Sanders made this much clear: For better or worse for the party, he can still own the Democratic debate. And, on this night, the Democratic debate stage.

The questions were about him. The answers were about him. The acoustics were about him. (“You don’t have to yell,” Ryan said at one point.) A viewer with the sound off would have had no trouble guessing which candidate many rivals were aiming at. “Do you believe Sen. Sanders is too extreme to beat President Trump?” a CNN chyron read.

Many Democrats fear not only that the answer is yes but also that merely entertaining the kinds of policies Sanders and Sen. Elizabeth Warren are pushing jeopardizes the party’s electoral fortunes. On health care in particular, moderates both inside and outside the two-dozen-strong presidential field have sounded alarms about how voters will respond to promises of dismantling private insurance.

“We can go down the road that Sen. Sanders and Sen. Warren want to take us, which is with bad policies like Medicare for All, free everything, and impossible promises that will turn off independent voters and get Trump reelected,” former Rep. John Delaney predicted Tuesday night, before ticking off the surnames of past Democratic presidential losers. “That’s what happened with (George) McGovern, that’s what happened with (Walter) Mondale, that’s what happened with (Michael) Dukakis.”

After an exchange over immigration, Ryan warned that the unyielding progressive tilt of the night’s debate was dangerous politics.

“Now, in this discussion already tonight, we’ve talked about taking private health insurance away from union members in the industrial Midwest, we’ve talked about decriminalizing the border, and we’ve talked about giving free health care to undocumented workers when so many Americans are struggling to pay for their health care,” he said. “I quite frankly don’t think that that is an agenda that we can move forward on and win.”

From their centrally located lecterns, Sanders and Warren, sharing the debate stage for the first time, formed a persistent tag team, quickly dispelling any notion that they might snipe at each other.

Although either’s path to the nomination probably depends on consolidating progressive support, neither has seen much upside in attacking, sustaining a peace born of broadly shared policy goals and a friendship that aides describe as genuine.

“Giant corporations and billionaires are going to pay more,” Warren said of the health care vision she shares with Sanders, in a line either could have uttered. “Middle-class families are going to pay less out of pocket for their health care.”

Their mutual nonaggression was notable, if unsurprising. Sanders’ poll numbers of late have been middling, with Warren appearing to siphon support among some of the party’s most liberal voters, even if their coalitions do not always overlap. (Warren’s base tends to be older, more female and more educated, while Sanders remains especially popular with younger voters.)

Still, the two can be contrasts in style and substance. Sanders speaks of wide-scale revolution; Warren has self-branded as the candidate with a plan for everything. Sanders’ best-known campaign medium is the megarally; Warren has often subsisted on smaller events, defined by personal voter interactions and winding lines for photographs. Sanders aligns himself with democratic socialism; Warren says she is “a capitalist to my bones.”

On Tuesday, Warren declined a moderator’s invitation to label herself “the safer choice” when asked if she was calling herself a capitalist to make a point.

“It’s my way of talking about I know how to fight, and I know how to win,” she said.

In another exchange, as Warren tried to respond to Delaney’s criticism of her trade plan, Sanders briefly jumped in, before being told to wait his turn.

“Oh, I’m sorry,” he said, deferring to his Senate peer.

Soon after, he planted himself firmly on Warren’s side.

“Elizabeth is absolutely right,” he said.

Yet if Warren’s steady rise in recent months has threatened Sanders’ hold on the hearts and minds of some progressives, he demonstrated repeatedly Tuesday that his political brand is to be underestimated at his detractors’ peril, regularly earning ovations from the crowd in Detroit.

After another more moderate rival, former Gov. John Hickenlooper of Colorado, suggested that the Sanders agenda would effectively “FedEx the election to Donald Trump,” Sanders reminded viewers that he is polling well against the president.

“If we’re going to force Americans to make these radical changes, they’re not going to go along,” Hickenlooper said.

He spotted Sanders stewing at the implication that those radical changes were not what people wanted. The senator began to lift his arms in protest.

“Throw your hands up!” Hickenlooper said, urging on the reaction.

And Sanders did just that, and the people roared.