Former Vice President Joe Biden, Sens. Elizabeth Warren (D-MA) and Bernie Sanders (I-VT) were just three of 10 candidates seeking the Democratic presidential nomination on stage in Houston on Thursday night.

But once they got past opening statements, seven candidates stood silent, as the current frontrunners debated the future of the country’s healthcare system.

Biden, who has held steady at the top of the polls since his entrance into the race in April, hesitated for a moment before launching into not-so-subtle attacks on Warren and Sanders. But when asked about his plan to build on the Affordable Care Act, former President Obama’s signature health care policy, Biden took the opportunity to criticize both his progressive rivals, who have been inching up on his lead for several months.

“It costs $740 billion. It doesn't cost $30 trillion,” Biden said before launching into Warren. “How are we going to pay for it? I want to hear that tonight. My distinguished friend, the senator on my left, has not indicated how she pays for it and the senator has, in fact, come forward and said how he's going to pay for it, but it gets him halfway there. There's a lot of things that need to be done.”

Warren, who evoked Obama’s name in her own response, fired back.

“The question is, how best can we improve on it?” Warren said about fixing the country’s health care system. “I believe the best way we can do that is we make sure that everybody gets covered by health care at the lowest possible cost. How do we pay for it? We pay for it, those at the very top, the richest individuals and the biggest corporations, are going to pay more. and middle class families are going to pay less. that's how this is going to work,” she said.

Biden-world spent the week laying the groundwork for their boss’s line of attacks the ABC debate. In a briefing with reporters on Thursday afternoon, three senior campaign officials previewed a strategy seemingly tailored to draw contrasts between the former vice president and his two liberal rivals in the field’s top tier.

“We’re going to need more than just plans—we need action,” said one official, echoed moments later by a colleague: “Plans are great, but you have to get things done.”

While the officials didn’t explicitly name Warren, the implication was clear that Biden sees the senator’s “I’ve got a plan for that” moniker as heavy on policy and light on the kind of hard accomplishments that the former six-term senator can boast.

“This race is not just about plans, it’s about getting things done for people,” one official said. “There’s a difference between talking about change and getting it done”

Sanders, whose Medicare-for-All plan has been a hallmark of his candidacy, didn’t miss a chance to dig into the current frontrunner.

“Let us be clear, Joe, in the United States of America, we have spending twice as much per capita on health care as the Canadians or any other major country on earth,” Sanders said.

“This is America,” Biden plainly replied.