Hillary Clinton's Iowa edge is gone.

Bernie Sanders leads the former secretary of state for the first time among Iowa Democrats likely to caucus in February, according to a new Quinnipiac University poll unveiled Thursday morning — the latest in a string of surveys that show a tightening race in the Hawkeye State.

The Vermont senator's advantage is within the margin of error — he took 41 percent compared with Clinton's 40 percent — and another 12 percent said they would support Vice President Joe Biden, who has yet to declare his 2016 intentions. (Former Maryland Gov. Martin O'Malley picked up 3 percent, while no other candidate registered above that mark, and 3 percent were undecided.)

But the shift is a significant one, coming on the heels of polls showing Sanders edging Clinton in New Hampshire, too. Together, the results suggest a candidate reeling from the controversy over her emails and struggling to put down a rebellion on her left flank.

While Clinton remains the front-runner for the nomination, and pollsters caution against reading too much into one survey, the results reflect serious movement for Sanders: He trailed the former secretary of state by a 52-33 percent margin in Quinnipiac's last poll of Iowa's likely Democratic caucus-goers, in July.

Clinton fared better in the latest NBC News/Marist polling of Iowa released last weekend, drawing 48 percent to Sanders' 37 percent. (With the vice president in the mix, Clinton stood at 38 percent, Sanders at 27 percent and Biden at 20 percent.)

Thursday's less favorable results are unlikely to surprise many in her Brooklyn headquarters: People close to Clinton's camp have recently been warning that Sanders could win both Iowa and New Hampshire before her massive organizing infrastructure kicks in among the next wave of nominating contests on March 1, when Clinton hopes to sew up the nomination. Her allies have also long noted that no non-incumbent candidate has broken the 50 percent mark in the Iowa caucuses other than Iowa's own Tom Harkin in 1992.

But the new Quinnipiac poll is nonetheless likely to send shockwaves through the Democratic establishment, which is increasingly nervous about Clinton's inability to put the email flap to rest, and worried about her seeming difficulty connecting with voters.

The fact that Thursday's result effectively shows a tie will hardly quiet the doubters, particularly given Clinton's heavy investment in her Iowa field operation — she has 78 paid organizers in the state, compared with more than 50 for Sanders — and her consistent lead until now.

A wide range of donors and strategists close to Clinton have expressed their dissatisfaction with her response to questions about her email use. But many in and around the Brooklyn headquarters said on Tuesday and Wednesday that Clinton's forthright apology — she told ABC News' David Muir on Tuesday, "That was a mistake. I’m sorry about that. I take responsibility." — could help stanch the bleeding.

Clinton supporters can take some solace in her enduring advantage among Iowa's women. Clinton leads Sanders to 49 percent to 35 percent among female likely caucus-goers, with 9 percent for Biden; though among men, Sanders leads 49 percent to 28 percent, with 16 percent for Biden.

And she remains popular with Iowa Democrats as a whole. Likely caucus participants said they have a favorable view of Clinton by 76 percent to 20 percent, earning trustworthiness marks of 64 percent to 30 percent and 78 percent to 18 percent saying she cares about their problems. By a count of 92 percent to 7 percent, voters said the former secretary of state has strong leadership qualities and 89 percent said she had the right temperament to tackle an international crisis, compared with 9 percent who did not think so.

But Sanders fares better. He drew a higher net favorability rating of +72 points (78 percent to 6 percent), and a higher share (86 percent to 4 percent) of those saying he is trustworthy than they did of Clinton. By a count of 85 percent to 5 percent, people said the senator cares about their issues. Asked about Sanders' leadership qualities, 76 percent said they were strong, compared to 9 percent who said they were not. On his temperament in times of crisis, voters approved of him by 65 percent to 15 percent.

Biden drew a net favorability rating of +70 points (79 percent to 9 percent), while 91 percent said he is honest and trustworthy, compared to 5 percent who did not think so. By a count of 84 percent to 11 percent, likely caucus-goers said Biden cares about the needs and problems of people like them. On the leadership front, 81 percent to 14 percent gave him high marks, while in terms of his ability to handle crises, 81 percent to 13 percent said they approved of his capabilities.

A majority of those surveyed — 54 percent to 33 percent — said that they would rather the party's candidate have experience in Washington than not.

The poll was conducted in the weeks around Labor Day, from Aug. 27-Sept. 8, surveying 832 likely Democratic caucus participants in the Hawkeye State via landlines and cellphones, with a margin of error of plus or minus 3.4 percentage points.