As more former aides shared stories of sometimes-abusive behavior, U.S. Sen. Amy Klobuchar vowed Friday to improve relations with her staffers.

The Minnesota presidential candidate is trying to rise from a large field of competitors as stories about her treatment of employees long shared privately among Democratic operatives and insiders are spilling into the open. Former employees of her Senate office and previous political campaigns have anonymously described to BuzzFeed, the New York Times and now the Star Tribune, many examples of behavior by Klobuchar they considered abusive, bullying and demeaning.

"I'm incredibly proud of the work our staff has done and I would not be here without amazing staff," Klobuchar said in a statement to the Star Tribune. "I know I can be tough, I know I can push people too hard, and I also know I can do better — and I will."

Klobuchar did not grant an interview for this story.

Among veterans of Klobuchar's employ, even those who defend her acknowledge an intense work environment.

"A lot of what's been said about working for Amy is true," said Zach Rodvold, who worked on Klobuchar's first U.S. Senate campaign in 2006 and ran her Minnesota office from June 2007 to September 2009. "I just don't see it as something that's disqualifying for running for president."

Rodvold, now district chief of staff to Rep. Dean Phillips, said he saw Klobuchar lose her temper, remembers her once throwing a pen in frustration, and said her expectations were at times unreasonably high. But he said she could also be funny, charming and charismatic, and that in his estimation she worked harder than anyone on her staff. Last month, Rodvold brought his family to Klobuchar's presidential campaign kickoff in Minneapolis.

"The best way I can describe it is sort of like Navy SEALs training. It's not intended to be fun. It's hard. But what you get from it is you become very, very good at what you do," Rodvold said. Like a number of Klobuchar's defenders, Rodvold said he thinks views of Klobuchar's leadership style are influenced by different standards for male and female bosses.

The Star Tribune interviewed four former Klobuchar staffers who all said her treatment of subordinates regularly went beyond what they considered acceptable even for a tough, demanding boss. They described similar kinds of behavior: Frequent angry outbursts over minor issues, regular criticisms and admonitions in front of others, office supplies or papers thrown in anger, cutting remarks and insults on a nearly constant basis, waking up to long strings of e-mails from Klobuchar sent late at night or in the early morning.

All shared those observations on the condition they not be named in this story, for fear of reprisal.

"You'd wake up to a string of four, five, six, seven, eight e-mails of increasing anger, with everybody copied," said one. "It was, 'This is the worst thing I've ever seen. Naive. Stupid. Awful.' It was just this vitriol. You didn't wake up to it every single day, but it was enough that my stomach just clenched every morning the second I woke up."

Another former staffer also described frequent late-night or early-morning e-mails from Klobuchar when she was upset about something: "Very personal attacks day after day. How long can you be called an idiot before you believe it?"

One of the former staffers, a woman, was angered by defenses of Klobuchar on feminist grounds. The source said she didn't think feminism excused bullying.

Two of the former staffers described an office constantly on edge, with senior employees usually either containing or anticipating Klobuchar's anger. One said Klobuchar was hardest on her top staffers and usually nicer to junior staffers and interns. Turnover was rapid; the website LegiStorm, a Congress-focused research group, currently ranks Klobuchar's office turnover as third highest in the U.S. Senate.

Klobuchar has pointed out that a number of her closest aides have worked for her for long periods of time. Many went on to important jobs in the Obama administration, other congressional offices and political operations, top law firms and major corporations around the country. Top staffers in U.S. Senate offices can make into the low six figures, with less senior or high-ranking staffers earning in the upper five figures.

Many politicians at high levels, men and women both, are privately known to be very hard to work for. Horror stories about working for Klobuchar have long circulated in political and media circles in Washington and Minnesota. The reluctance of former staffers with firsthand experience to identify themselves kept the stories out of the public eye, but the glaring scrutiny of a presidential campaign changed that.

To date, all of Klobuchar's most critical former staffers in this and other stories have remained anonymous.

Published stories about Klobuchar's alleged mistreatment of employees both preceded and followed her entry into the contest for the Democratic nomination. It was an otherwise successful rollout: a snowy announcement along the Mississippi River garnered a wave of largely favorable national press, with Klobuchar winning praise from many early-state Democrats, pundits and even some Republicans for her pragmatic tone, results-driven approach, gregarious style with voters and track record of electability.

Democratic voters in Iowa and New Hampshire, who will weigh in first as the nominating contest gets going early next year, have been reading and circulating the coverage of Klobuchar's treatment of employees.

"If not for that cloud, I think she would have a really great shot at Iowa. She may yet," said Pat Rynard, a former Democratic campaign operative who now runs the Iowa Starting Line website, which covers the Iowa caucus.

Mike Lewis, an attorney in Concord, N.H., co-hosted a recent house party for Klobuchar. He said she's currently among his top choices, and he said he's wary of anonymous allegations about a Democratic contender in the approach to an election many see as vitally important to the country's future.

"In an era of disinformation, people are going to wait to hear more and assess," Lewis said.

Last weekend, 66 former Klobuchar staffers from her time in the Senate and her previous tenure as Hennepin County attorney signed a letter posted on the website Medium that said positive anecdotes about Klobuchar as a boss had been neglected in the recent coverage.

"I wouldn't say she was abusive at all. She generally is a nice, kind, caring woman who wants to do well," said Christi Mayer, who worked two jobs in Klobuchar's D.C. office in 2007-08, director of scheduling and director of administration. "She's tough. And I don't see anything wrong with that."

Before she worked for Klobuchar, Mayer worked several years for a four-star Army general, Gen. Barry McCaffrey. After she left Klobuchar's office, she worked for a time for Sen. Kirsten Gillibrand, another Democratic presidential candidate, whose office Mayer said was similarly rigorous.

"I worked for tougher people," Mayer said.

Deb Calvert worked as Klobuchar's state scheduler for four years. While it was "a very hard job," she said the expectations reflected the senator's own personal work ethic. She said Klobuchar was very loyal and dedicated to her staff, in her experience.

None of these sources denied that working for Klobuchar was often tough and draining, and they stressed they did not mean to discount the experiences of others.

Mychal Vlatkovich, who worked two stints as Klobuchar's Minnesota-based press secretary, said she taught him to function in an intense, high-pressure environment.

Vlatkovich is now communications director to Minneapolis Mayor Jacob Frey. Of his time with Klobuchar, he said: "I did feel gratitude — you talk about accelerating your career, I couldn't have jump-started it any better than I did under her management."