Pete Buttigieg on Thursday took a swipe at fellow 2020 hopeful Elizabeth Warren, knocking the Massachusetts senator for a lack of transparency about how she’d pay for her “Medicare for All” plan.

During an interview on CNN’s “The Lead,” anchor Jake Tapper pointed out that Buttigieg first appeared to take a dig at several of his opponents in a Washington Post op-ed rolling out his own health care plan.

In the editorial, the mayor of South Bend, Ind., wrote that his plan would allow the country to achieve “universal health care and a public alternative without raising taxes on the middle class.”

Buttigieg goes on to say in the op-ed: “Anyone who lets the words Medicare for All escape their lips should tell us just as plainly how they plan to get there.”

Tapper and Buttiegieg also referenced Warren’s recent appearance on Stephen Colbert’s “The Late Show,” during which the senator continually dodged answering explicitly whether the middle class would see its taxes go up, despite Colbert’s calling her out for skirting the specifics.

Critics of single-payer health care seized on Warren’s equivocation, which Buttigieg noted is out of the ordinary for the senator and former law professor. “Senator Warren is known for being straightforward and was extremely evasive when asked that question,” he said.

He continued: “If you’re proud of your plan and it’s the right plan, you should defend it in straightforward terms. It’s puzzling when everybody knows the answer to that question of whether her plan and Senator [Bernie] Sanders’ plan will raise middle-class taxes is ‘yes.’”

It’s just the latest instance of Buttigieg beginning to draw sharper contrasts with his rivals as his campaign appears to have stalled a bit among the 2020 field. In the days since last week’s primary debate in Houston, Buttigieg also sparred with former Rep. Beto O’Rourke over O’Rourke’s insistence that he would impose a mandatory federal buyback of assault weapons if elected president.

Warren and Buttigieg fall into different camps among Democratic White House contenders when it comes to health care. While Warren has been among the few candidates who still backs Sanders’ single-payer model, Buttigieg has taken a more moderate lane, releasing a plan on Thursday that he has dubbed “Medicare for All Who Want It.”

In Buttigieg’s plan, he elaborates on ideas he has touched on during his presidential campaign, such as building on Obamacare and creating a “public option” to compete with private insurers.

The price tag of a single-payer plan like “Medicare for All” has been among the chief criticisms of its opponents, who have also bashed it because such a system would eliminate private insurers. But Warren and Sanders have defended the idea by arguing that Americans would end up saving in the long run by having their total out-of-pocket costs reduced. Warren has also said that her proposed tax on the ultrawealthy would help shoulder the costs.

Buttigieg said on Thursday that he is confident his proposal is the smartest way to reshape the health care market.

“We’re seeking to attack the problem of affordability from several angles,” he explained. That means looking at insurance “but also looking at what’s driving those costs in the first place. And I really do believe the public alternative will be better.”

And, he added, it’s possible that his plan could “well be the glide path that leads to a Medicare for All environment.” He contended that he wants people to have a choice between his public option or maintaining their current coverage through a private insurer.

“I think ours will be better,” he asserted. “If we’re right, Americans can decide that for themselves.”