The top three Democratic candidates were put on defense during Tuesday night’s debate, with Joe Biden, Elizabeth Warren, and Bernie Sanders all facing pointed questions about their age, health and how those factors could affect their electability and potential presidency.

The line of questioning started with Sanders, I-Vt., who just returned to the campaign trail after suffering a heart attack earlier this month. The 78-year-old was asked how he could “reassure” Americans that he was up for the task.

“We are going to be mounting a vigorous campaign all over this country. That is how I’m going to reassure the American people,” Sanders said while thanking voters, friends and fellow Democratic primary candidates for their support. “I’m so happy to be back here with you this evening.”

Next came Biden—whose age has been a topic of conversation and criticism over the past several months on the campaign trail. CNN’s Erin Burnett quoted former President Jimmy Carter, who said that he wouldn’t have been able to start a presidential term at the age of 80, and pressed Biden why he thinks he could handle the pressure.

“Because I watched it, I know what the job is, I’ve been engaged,” Biden, 76, said, adding that “one of the reasons” he is running for president is his age—and with that, comes “wisdom.”

“We need someone in office this time around who on day one, on the world stage, can command respect from world leaders and know exactly what needs to be done to get this country back on track,” he said. “That’s one of the reasons why I decided to run this time because I know what has to be done. I’ve done it before, I’ve been there.”

He added: “I will not need any on the job training.”

Biden, who has grappled with sustained critical media coverage of a string of gaffes on the campaign trail, then vowed to release his health records, along with his tax records, before the Iowa Caucuses in January—the first contest of the 2020 primary season.

“I’m the only guy who’s released anything up here,” he scoffed.

Warren, D-Mass., who is 70, brushed off her age, when asked to respond.

“I say I will outwork, out-organize, and outlast anyone and that includes Donald Trump, Mike Pence or whoever the Republicans get stuck with,” she said.

Meanwhile, President Trump, who is 73, has said he feels “young” and is ready for another term of his administration.

“I feel like a young man. I am a young, vibrant man,” Trump said in April.

Should Trump be re-elected, he would be 74 on Jan. 20, 2021—Inauguration Day. Should the presidency go to one of the elder Democrats in the field—Biden would be 78; Sanders would be 79; and Warren would be 71.

But the CNN and New York Times moderators shifted to the other end of the spectrum, pointing to Rep. Tulsi Gabbard, D-Hawaii, for her young age of 38.

“It’s not fair to ask these three about their health and their wellness,” she said of the questions to Biden, Sanders and Warren. “Who is fit to serve as commander-in-chief?”

Gabbard said that she was, and further challenged the moderators to ask every candidate on the stage about their age and health—a suggestion that was ignored.