“You have to wonder whether she peaked too soon,” former Iowa Lt. Gov. Patty Judge, co-chair of the advocacy group Focus on Rural Iowa, said of Warren. “In Iowa, she is wearing some — [it's] like she established her endorsers and her delegates and that’s all there is.”

While the top-polling candidates are sure to rise and fall before the Feb. 3 caucuses, a dozen Democratic activists, county chairs and strategists in the state said Warren is no longer viewed as the prohibitive frontrunner there. Her performance reflects her struggles of late nationally, including one poll out Tuesday that showed her support cut in half in the span of a month.

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.

Warren did not air TV ads in Iowa until this month. While she was dark, Buttigieg poured more than $2 million in TV spots that went after Medicare for All, saying he would not dictate people’s health insurance choices.

“It’s a subtle but strong message,” said Matt Paul, a longtime Democratic Iowa strategist who is uncommitted in the race.

In addition to the ads up now, Warren has reserved more than $2.4 million in TV air time in January, according to Advertising Analytics, a political ad tracking firm.

Biden, who has lost ground as the frontrunner in the state since he entered the race, is hoping a rebound he’s seeing in some national polls will extend to Iowa. Last weekend, he won the coveted joint endorsement of former Gov. Tom Vilsack and his wife, Christie.

Tom Vilsack, who served with Biden in the Obama administration, said in an interview that Biden has demonstrated he can appeal to voters in the Rust Belt, which will be critical to defeating Trump.

“People know him and that’s one downside of his campaign — he’s not the new kid on the block. But you can take a lot of confidence and security that he’s gone through the wringer and people still like him,” Vilsack said. He added that he wasn’t worried that Biden has failed to draw the kind of large, enthusiastic crowds that Warren and Buttigieg have in the state. “I don’t feel like I need to jump up and down and hoot and holler, I know Joe.”

Biden is embarking on an eight-day bus tour across 18 Iowa counties and just launched a new series of ads. A super PAC supporting him plans to heavily invest in the state on his behalf.

“I think reports of the vice president’s demise are premature,” said Paul. “That’s how quickly this can change. Welcome to the majors. That’s what these people have to get used to. It can change quickly and it can change again.”

For now, it’s Buttigieg who is attracting the large crowds and on-the-ground enthusiasm in Iowa.

Jeremy Dumkrieger, chair of the Woodbury County Democrats, attributed Buttigieg’s rise in part to his speech at the Liberty & Justice dinner earlier this month but also to his ability to connect with voters one on one.

“I think people look at Pete as sort of ... rooted in small town values,” said Dumkrieger, who is not endorsing in the contest. “I think Iowans like that. I think he’s a little bit relatable that way. ... There’s a small town Mayberry feel to him.”

Alex Thompson contributed to this report.