Senator Amy Klobuchar’s nascent campaign is fending off a stream of stories from former staffers that she was a volatile, highhanded boss who often demeaned and humiliated people who worked for her. She has one of the highest rates of turnover in the Senate.

“Am I a tough boss sometimes? Yes,” she said in a recent CNN forum. “Have I pushed people too hard? Yes.”

The presumption that tough bosses get results — and fast — compared with gentler leaders is widespread, and rooted partly in the published life stories of successful C.E.O.s. Bobby Knight, the Indiana University basketball coach and author of “The Power of Negative Thinking,” was notoriously harsh, and enormously successful. So was Steve Jobs, the co-founder of Apple.

But researchers who study organizations, productivity and leadership styles attribute the achievements of such figures to exceptional ability. The research thus far has found no evidence to support the axiom that tougher bosses get better results.