Speaking to reporters in Council Bluffs on Sunday, Ms. Warren said that if Medicare for all has received little attention at her Iowa events, it’s because “I take whatever questions come my way” and the voters have had other concerns.

And she rejected the criticism, mostly lobbied by ardent progressives, that her plan waffles on an immediate push for enacting Medicare for all and ending private health insurance, as Mr. Sanders has long proposed.

In November, after Ms. Warren faced blowback for her proposal for $20.5 trillion in new spending over 10 years to enact Medicare for all, she surprised many by proposing an expansion of public health insurance as a first step — similar to the positions of rivals like Joseph R. Biden Jr. and Pete Buttigieg — and then achieving passage of Medicare for all by the end of her third year in office.

Ms. Warren’s campaign and its surrogates say that the type of insurance offered under their plan is more comprehensive than Mr. Biden’s and Mr. Buttigieg’s proposals, and that the Warren camp has provided more details on how to implement and finance a single-payer system than Mr. Sanders.

“I’m still with Bernie and we’re still there on Medicare for all,” Ms. Warren said in Council Bluffs. “I still think it’s the right place.”

But there are signs that her campaign is proactively seeking to calm fears about her health care proposal. Denise O’Brien, a rural community activist and prominent supporter of Ms. Warren’s from Atlantic, Iowa, said she and other supporters have been coordinating with the campaign to hold Medicare for all “listening sessions” in her town.

Ms. O’Brien said that she will soon hold her third event, and that community members have had several questions, particularly since Ms. Warren was pressed during the Democratic debate in October. The typical running order of the sessions, she said, is that a doctor who supports Medicare for all explains the health care insurance system and its pitfalls, while a campaign staff member lays out Ms. Warren’s position.