Marjorie Duske, the longtime Minnesota congressional aide who guided Amy Klobuchar through a challenging six-month stint as Minnesota's only U.S. senator, has stepped down as her chief of staff. Duske signed on as the Minnesota Democrat's top aide early last year, just as former Sen. Norm Coleman's term was expiring – but before Sen. Al Franken won the recount battle in July. "She was great," Klobuchar said Monday. "She had a very hard job." Duske was Klobuchar's third chief of staff in as many years, following Sean Richardson, a former aide to Rep. Patrick Kennedy, D-R.I., and Lee Sheehy, a former Minneapolis planning and economic development official who is now with the McKnight Foundation. Klobuchar said there is no mystery in the turnover. She described Richardson as a transitional leader who was brought in to help get her office up and running at the start of her term in 2007. Sheehy, who remains a Klobuchar confidant, returned to Minnesota a year ago to get married to longtime DFL activist Cathy Forciea, who once worked for the late Sen. Paul Wellstone. Duske, for her part, is returning to her specialty on the House Appropriations Committee, where she worked for 17 years. A longtime aide to former Minnesota congressman Martin Sabo (no piker at getting money for his state) Duske will now be working under committee chairman David Obey of Wisconsin.