COLUMBUS, Ohio — Sen. Elizabeth Warren confronted a cascade of pointed criticism from a trio of more moderate Democratic rivals Wednesday, as they sought to capitalize on a debate that saw the leading liberal candidate face intense scrutiny amid worry by her opponents that her momentum, money and energetic crowds are obscuring a hard look at her ideology.

Joe Biden lobbed some of his most biting charges at her, questioning her honesty and saying her Medicare-for-all health plan “is ridiculous, absolutely ridiculous.” South Bend, Ind., Mayor Pete Buttigieg and Sen. Amy Klobuchar (Minn.) stepped forward more assertively against Warren in the wake of persistent questions about Biden’s own strength as the more moderate standard-bearer.

“Last night she was more specific and forthcoming about the number of selfies she’s taken than about how her plan is going to be funded,” Buttigieg said on CNN.

“Show your math and say how you’re going to pay for Medicare-for-all,” Klobuchar said in a separate interview.

As the party’s fourth debate concluded, the Democratic primary contest opened a more robust and unpredictable clash over the ideological direction of the party, with moderates attempting to ignite the kind of passion that the liberal candidates have harnessed with large crowds and grass-roots donor networks. After months in which the race was largely static amid a crowded, free-ranging field, the nomination fight is showing signs of narrowing its focus to fewer candidates, divided into parallel feuds in the liberal and moderate wings of the party.

Warren (Mass.) is entering a crucial phase of her campaign, taking attacks from all sides for the first time since she ascended in popularity, and attempting to demonstrate she can withstand the kind of scrutiny that previously fell mostly on Biden, who until recently held an unchallenged lead in the polls. Yet as she attempts to coalesce support on the party’s left flank, Warren faces a renewed challenge from liberal Sen. Bernie Sanders (I-Vt.), whose debate appearance helped alleviate questions about his health and whose new endorsements and deep bank account have made clear he has no intention of leaving the race.

The left’s feud is replicated in the center, where Biden faces challenges from Buttigieg, Klobuchar and others.

“It’s the first time the candidates admitted that Warren is the front-runner. Nobody had onstage, next to her, pressure-tested her policies and statements before,” Ben LaBolt, the national press secretary for President Barack Obama’s 2012 campaign, said of the debate. “Biden has always been a fragile front-runner, and I don’t think you would call him the front-runner anymore. So if you are Buttigieg or Klobuchar, the most obvious play was to try to go after Biden supporters who seem more gettable now than they were six months ago.”

Biden on Wednesday also faced a striking problem for a former vice president with decades of Democratic connections: a lack of money. He only had $9 million cash on hand at the end of the third quarter, figures released late Tuesday showed. That was less than a third of the stockpile enjoyed by Sanders, Warren and Buttigieg, and the gap elevated fears of allies about his ability to compete if a contentious primary fight runs deep into next spring.

Biden on Wednesday dismissed concerns about his financing, and he pointed toward the advantage Warren and Sanders had in transferring money from their Senate accounts. He gave no hint to any cutbacks in spending, which included nearly $1 million for private charter flights in the third quarter. (Warren on Wednesday was spotted flying in coach on a commercial airline.)

The former vice president sought to focus instead on the lively squabble over Warren’s liberal policies, particularly on health care, where she has largely yielded to Sanders. As he and others did during the debate, Biden questioned how she would pay for Medicare-for-all’s significant costs.

Sanders, the author of the Medicare-for-all plan, has acknowledged it will require increased taxes. Warren supports his plan to extend coverage to everyone in the United States and abolish the private health insurance industry, but unlike Sanders she has yet to provide details about how she would pay for a bill estimated to cost $30 trillion over a decade.

Both assert that middle-class Americans would see lower costs overall. But economists have said it is impossible to make that guarantee given the details the candidates have put forward so far.

“It’s fascinating that the person with a plan for everything has no plan for the single most consequential issue in this election in the minds of the American people, across the board,” Biden told reporters here before heading into a union hall in Columbus. “And you know, credibility matters. . . . She’s going to have to tell the truth or the question will be raised about whether or not she’s going to be candid and honest with the American people.”

“I don’t want to pick on Elizabeth Warren,” he added. “But this is ridiculous. Absolutely ridiculous.”

Biden and his allies also ramped up their criticism of an answer Warren gave during the debate in which she said, “I think we ought to get out of the Middle East. I don’t think we should have troops in the Middle East.” She later clarified that she meant only combat troops.

“I was surprised last night in the debate one of my colleagues said we should remove all troops from the Middle East,” Biden said at a Wednesday afternoon event in Davenport, Iowa. “We can be strong and smart at the same time.”

Sen. Christopher A. Coons (D-Del.), who has endorsed Biden, said after the debate that Warren’s comment showed Biden was “clearly the stronger candidate in terms of being able to be commander in chief. She’s really not prepared for that role.”

On Wednesday, Warren’s chief campaign strategist, Joe Rospars, said the debate had illuminated Warren’s rise.

“Last night, in the face of more attacks from more candidates than anyone’s taken on any debate stage so far, Warren fought back by making her case for what really matters without descending into petty sniping,” Rospars tweeted. “It’s a pretty rare thing to see in politics.”

He also pointed to filings released Tuesday that showed Warren had $25.7 million on hand at the end of September: “She’s talked one-on-one with more than 70,000 people and isn’t funding her campaign by charging $1,000 to schmooze and take photos with rich people behind closed doors.”

While Biden was aiming directly at a candidate who has met and sometimes exceeded him in recent polls, the strategy for Butigieg and Klobuchar was somewhat more nuanced: to try to persuade voters who may be leaning toward Biden that they are better positioned to articulate a path forward for the party, first against the liberal candidates, and then against Trump.

Klobuchar on Wednesday remained focused on Warren and her health care plan.

“It’s incredibly expensive. And it cuts 149 million people off their current health insurance in four years,” Klobuchar said in a CNN interview Wednesday, reprising her comments from the night before. “She just needs to come out and say how she’s going to pay for it. That’s all. That’s what I’m saying. And we’re waiting to see it.”

Klobuchar also took issue with Warren’s tone.

“She has repeatedly said . . . things like, ‘You have to show you’re going to fight for things,’ and implying very clearly that those of us who have different approaches aren’t fighting,” she said. “I’m fighting. I just think I have a better way.”

Although Klobuchar is far behind many of the other candidates in the polls and fundraising, her hope lies in surveys that show most voters haven’t yet made up their minds and are willing to continue considering candidates.

The senator from Minnesota pitches herself as pragmatic and realistic; someone who, like Biden, can connect with white blue-collar voters, especially those in the Midwest. She has been campaigning heavily in Iowa and recently did a “Blue Wall Tour” of Pennsylvania, Michigan and Wisconsin — states that voted for Trump in 2016 after having sided with Democratic nominees for decades.

For his part, Buttigieg has grown more direct in his criticism of Warren over the past several weeks as he too focuses tightly on Iowa, a state that has catapulted past candidates to the nomination, most recently Obama. He has remained in the middle of the pack, lacking the opening that Biden’s stumbles could provide.

Both Buttigieg and Klobuchar claim to represent a sensible Midwestern approach, but from a younger generation than Biden’s.

“Right now you have a group of candidates who are positioned to capitalize if one of the front-runners falters in the early states,” said Jefrey Pollock, a Democratic consultant and pollster who runs Global Strategy Group and previously served as an adviser to the presidential campaign of Sen. Kirsten Gillibrand (D-N.Y.).

“An upset in Iowa or in New Hampshire or Nevada could reasonably open up a lane for someone new,” he added, pointing toward Buttigieg as well as Sens. Kamala D. Harris (D-Calif.) and Cory Booker (D-N.J.). “All will be looking to be the alternative in the reasonable common-sense candidate lane.”

The focus on Warren defused for now a continuing issue for Biden beyond his relative lack of money and supporter passion — the impact of questions about his son Hunter Biden’s decision to join the board of a Ukrainian gas company while Joe Biden served as the Obama administration’s point man in the country. Trump’s effort to prompt investigations of the Bidens is at the heart of the House impeachment inquiry.

Joe Biden said he wouldn’t have changed anything about his actions, including discouraging his son from joining the board, and had no regrets.

“No. No, I don’t,” he said Wednesday. “Because I never discussed with my son anything having to do with what was going on in Ukraine. That’s a fact.”

Sanders, meanwhile, enjoyed a positive jolt from the debate, his first formal appearance since having a heart attack two weeks ago. After the debate, two prominent congresswomen — Alexandria Ocasio-Cortez (D-N.Y.) and Ilhan Omar (D-Minn.) — endorsed Sanders, giving him another boost.

Holly Bailey in Davenport, Iowa, and Michael Scherer, Jenna Johnson and Amy B Wang in Washington contributed to this report.