Warren’s biggest gains have come since the last debate, so Tuesday's debate was the natural point for a more full-throated engagement from the other candidates. Until now, three elements central to Warren’s candidacy have received relatively little pressure from her opponents as she has slowly ticked up in the polls.

The first is whether the candidate of always having a plan can escape the question of Medicare for All’s cost that has haunted her candidacy for months. The second is the corollary character question about whether her refusal to cough up more details and numbers will damage Warren’s robust approval ratings. Finally, Warren has made strides to convince Democrats that she can beat Trump, but until Tuesday she hasn’t had to answer sustained attacks that her platform is too far left to win.

She seemed to hold up relatively well — no major slip-ups — but the arguments her rivals made against her are a harbinger of what’s to come this fall, after a relatively smooth ascent over the past several months.

Warren is often credited with running the most disciplined campaign, and she was clearly prepared for the evening’s offensive. Indeed, her most persistent critic, Mayor Pete Buttigieg, who has raised as much money as Warren but has only a fifth of the vote share to show for it, has been signaling for weeks that he would aggressively challenge her in Ohio.

Through three hours of sporadic attacks, Warren remained energetic (some voters had to be surprised to learn midway through the evening that Warren is 70 years old), occasionally cutting (“Medicare for all who can afford it,” she called Buttigieg’s plan), and unmoved by her interlocutors’ insistence that she confess to the true costs of her health care plan. (A direct question — “Will you raise taxes on the middle class to pay for it? Yes or no?” — was answered with references to “my principles,” the number of selfies she’s taken this year and anecdotes about the indignities of the modern medical system, but neither a yes or a no.)

The evening’s attacks began with the issue that has dominated all four Democratic primary debates — in fact, the issue that has dominated Democratic politics since FDR: how to achieve universal medical insurance in the United States.

Unlike Bernie Sanders, the progenitor of the Warren policy, the Massachusetts senator has declined to explain how she would pay for her plan to transition all Americans into the popular Medicare program that now only serves people over 65. Her refusal to detail the costs was turned into cudgel by Buttigieg and others to question not just her policy but her honesty.

“We heard it tonight,” said Buttigieg when asked whether Warren was “evasive.” “A yes or no question that didn't get a yes or no answer. Look, this is why people here in the Midwest are so frustrated with Washington in general and Capitol Hill in particular. Your signature, senator, is to have a plan for everything. Except this.”

When Sanders butted into the conversation, it was as a foil that Warren’s attackers could use. "I do think it is appropriate to acknowledge that taxes will go up,” said Sanders, one of the few candidates who declined to press Warren.

“Well, at least that's a straightforward answer,” said Buttigieg.

“Bernie is being honest," added Sen. Amy Klobuchar. “We owe it to the American people to tell them where we will send the invoice.” Warren responded by trying to explain that her life’s work of studying “why hard-working people go broke” convinced her that only Medicare for All could address spiraling health costs that bankrupt Americans.

“I appreciate Elizabeth's work," Klobuchar said wryly. “But, again, the difference between a plan and a pipe dream is something that you can actually get done.”

When the discussion turned to Warren’s wealth tax, candidates seized on the same perceived vulnerabilities: She is too idealistic and too dismissive of other ways to achieve the same goal. Andrew Yang noted that a wealth tax had been tried and abandoned in Germany, France, Denmark, and Sweden.

Klobuchar seemed peeved that Warren was too rigid in her policy thinking. “I want to give a reality check to Elizabeth,” she said. “No one on this stage wants to protect billionaires. Not even the billionaire” — Tom Steyer — “wants to protect billionaires. We have different approaches. Your idea is not the only idea.”

Beto O’Rourke leveled a new criticism. “Sometimes Sen. Warren is more about being punitive and pitting some part of the country against each other, instead of lifting people up,” he said. (An incredulous Warren retorted, “I'm really shocked at the notion that anyone thinks I'm punitive!”)

Much of the pile-on concerning health care was not really about the policy, but instead about Warren’s character. This is a familiar script. In the fall of 2007, when Barack Obama was struggling to gain ground against Hillary Clinton, his advisers told him he would never win a white paper war against a policy wonk like Clinton, and he needed to turn the race to a contest about character. That is precisely what Obama did in October and November of that year, when he subtly raised issues about whether Clinton was honest. (Two of the architects of that strategy, Larry Grisolano and the Benenson Strategy Group, now work for Buttigieg.)

There are obvious differences between 2007 and 2019. Clinton’s reputation had been battered during her husband’s presidency, while Warren’s favorability ratings are strong. But still, the strategy is familiar.

There were stretches Tuesday night when Biden, the co-front-runner, faded from the conversation as Klobuchar, Buttigieg, and O’Rourke engaged Warren. But in the final hour the two leaders in the race had a clash that was akin to an after-credits scene of a superhero movie that sets up the next film. Biden bragged that he was the only one on stage who has accomplished major legislative achievements, a claim that arguably has some merit.

Unsurprisingly, Warren pointed to her work, before she was a senator, helping pass the Consumer Financial Protection Bureau. Biden was quick to add that he personally rounded up votes for the legislation.

“I convinced people to vote for it,” he insisted.

Warren refused to cede an inch of credit to him for her signature accomplishment.

“I am deeply grateful,” she said slowly and with what may have been a smirk, “to President Obama, who fought so hard to make sure that agency was passed into law.”

Biden grinned widely, seeming to almost admire her ploy.

They both had reason to grin. By the end of the night, things were back to where they started: with Biden and Warren on top. But after months of Biden receiving the scrutiny and criticism of a front-runner, it's now Warren being chased by a pack of much more aggressive rivals.