Democratic National Committee Chairman Tom Perez speaks to a crowd of supporters at a unity rally in Salt Lake City on April 21, 2017 . (George Frey/Getty Images)

Democratic National Committee CEO Jess O’Connell is leaving the job after less than a year, the latest shake-up for an organization that has won of a string of elections while struggling with internal divisions and grumbling, cash-starved state parties.

O’Connell, who joined the DNC last May from Emily’s List, announced her departure in a Monday night email, first obtained by NBC News. “I’m proud to have helped to rebuild our party at a time when we needed it most,” O’Connell wrote, while not saying why she was choosing to leave.

In a statement to The Washington Post, DNC Chairman Tom Perez said that O’Connell joined the party “when it needed her most” — months after he won a lengthy and sometimes bitter contest to lead it.

“Her leadership brought a laser-like focus on winning elections up and down the ballot,” Perez said of O’Connell. “She helped build our Every Zip Code Counts strategy, oversaw unprecedented programming and support for state parties and campaigns, renewed our focus on data and technology, and helped lead us to 100+ victories in elections all across the country in 2017. ”

O’Connell’s tenure at the DNC was seen, and promoted by the party, as a turnaround. She came into the job shortly before the party lost the highest-profile special House election of 2017, in suburban Atlanta, and presided over strategic — and often quiet — investments in other races that went the party’s way.

In November, the DNC parted with its chief fundraiser, the first dramatic response to the party’s 2-1 lag behind its Republican counterpart. But O’Connell remained front and center in the party’s messaging; in a Jan. 25 announcement about new DNC security officer Bob Lord, O’Connell was cited as a member of a “strong leadership team.”