The Iowa Democratic officials aren't predicting Warren's demise — far from it. She is widely acknowledged as having assembled the best organization in the state, a vital component of success.

But some Democrats expressed concern that Warren, however unfairly, has been hurt by her embrace of Medicare or All, including her initial refusal to say whether it would mean a middle-class tax increase.

Then, the $20.5 trillion health care proposal Warren rolled out earlier this month only invited more questions, and she responded unevenly, making uncharacteristic gaffes when trying to explain it. In Iowa earlier this month, she said only billionaires' taxes would go up to pay for Medicare for All, but her plan stated otherwise. A few days later in Raleigh, North Carolina, Warren said that immigration reform would bring in $2 trillion to help fund single-payer health care — but her plan estimated it would generate $400 billion. Her campaign had to clarify both remarks.

“The only conversation happening among undecided caucus-goers is about health care,” said Polk County chairman Sean Bagniewski. “The thing about Iowa, we’re known for being an agricultural state, but we’re one of the insurance capitals of the world. I think people are more detail oriented and policy oriented in Iowa, because a significant amount of our workforce is in the insurance industry.”

The Warren campaign has been quietly frustrated that the same level of scrutiny hasn't been applied to her rivals, including Biden, Buttigieg, and Sanders, who have not released equally detailed proposals on how they would pay for their own health care plans.

Warren’s drop in the polls could simply reflect the travails of a frontrunner whose numbers drop in the face of scrutiny, but then bounce back. Biden went through that cycle in recent months, losing ground to Warren in national polls before rebounding.

"We’re in this race to build a grass-roots movement for big, structural change,” Warren’s Iowa spokesman Jason Noble said. “That’s what we are doing and will continue to do in Iowa and across the country."

The results of the latest flagship Iowa Poll, released earlier this month, are perhaps the most telling sign of a shift for Warren. She fell by 6 points, the first time since December 2018 that her numbers declined in the quarterly survey. Buttigieg was in the lead, with Warren, Sanders and Biden essentially tied for second.

The dynamics in Iowa are a microcosm of the senator’s national struggles. In a national Quinnipiac poll released Tuesday, Warren plummeted to 14 percent support, down from 28 percent in October when she led that organization's poll. The Tuesday survey also found that support for Medicare for All dropped to 36 percent, from 43 percent support in March.