A new Quinnipiac University poll shows Democratic presidential candidates Bernie Sanders and Hillary Clinton in a virtual tie among likely Democratic caucusgoers in Iowa.
Sanders has made huge gains since Quinnipiac’s July 2 poll, when he had just 33 percent support to Clinton’s 52 percent. In the most recent poll, taken from August 27 to September 8, he picked up eight percentage points to threaten Clinton, with 41 percent to her 40 percent, a difference within the margin of error.
Vice President Joe Biden, who is considering a presidential bid, also moved up in this poll, netting 12 percent support, compared to seven percent in June. Former Maryland Gov. Martin O’Malley had three percent support, and another three percent of likely Democratic caucusgoers say they’re undecided.
Sanders’ upward momentum stems from his message, which is “more in line with disproportionately liberal primary and caucus voters,” said Peter Brown, assistant director of the Quinnipiac poll. A greater portion of voters who describe themselves as “very” liberal picked Sanders (59 percent) over Clinton (29 percent).

Sanders also did better among men, winning 49 percent of their support to Clinton’s 28 percent. Clinton, on the other hand, did better among women, leading Sanders 49 percent to 35 percent.

He pulled ahead of Clinton in a NBC/Marist poll of New Hampshire last week, beating Clinton 41 percent to 32 percent.

While Clinton’s numbers on personality traits are still fairly strong – 78 percent rated her as favorable, and 64 percent said she was honest and trustworthy – Sanders and Biden both had lower negatives. While 20 percent of likely Democratic caucusgoers did not have a favorable impression of Clinton, just six percent said the same of Sanders and nine percent of Biden. A full 30 percent of voters said Clinton is not honest and trustworthy, but just five percent said that of Sanders and Biden.

Clinton scored better than both on strong leadership qualities, with 92 percent for Clinton, versus 76 percent for Sanders and 81 percent for Biden, and 92 percent said she has the temperament and personality to handle an international crisis. Just 65 percent said the same of Sanders and 81 percent of Biden.

Some of Sanders’ strongest supporters are college-aged voters and young adults. Sixty-seven percent said they’d vote for him, versus just 29 percent who said they would vote for Clinton. Yet those voters can’t exactly be counted on to show up to caucus. Take Mr. Obama’s 2008 victory in Iowa: 17 percent of caucus attendees were between the ages of 17 and 24 years of age, while sixty percent of all Democratic caucusgoers that year were older than 45 years old.

Jherron Sutton, a 19-year-old student at Grinnell College who is originally from Maryland but is now a registered voter in Iowa, explained why Sanders appealed to him.

“[H]e came across as genuine, and he has not been made into a celebrity like people such as [Donald] Trump and possibly even Clinton,” she told CBS News political digital journalist Kylie Atwood. She also liked Sanders’ message about helping middle-class families and making college education affordable when she heard him speak at Grinnell last week.

Still, Sutton said she hasn’t figured out whether she will caucus in February.

The poll surveyed 832 likely Iowa Democratic caucus participants and has a margin of error of plus or minus 3.4 percentage points.

© 2015 CBS Interactive Inc. All Rights Reserved.