WASHINGTON — The CEO of the Democratic National Committee is leaving after less than a year on the job, NBC News has learned.

Veteran Democrat operative Jess O’Connell took the helm of the DNC last May with a mandate to help newly installed Chairman Tom Perez turn around a troubled party organization that was struggling after years of neglect and a brutal 2016 that included accusations of favoritism in the primary between Hillary Clinton and Bernie Sanders, the hacking of internal emails, and the loss to President Donald Trump.

O’Connell will leave the party stabilized, if not yet fully recovered, after wins last year in Virginia and Alabama, and her decision to leave is a personal one, a DNC official told NBC News, timed to cause minimal disruption ahead of November's midterm elections.

But O'Connell's departure comes just months after the DNC ousted its finance director following a period of weak fundraising, as well as a shakeup last year that reignited tensions with Sanders' allies. Still, the party has found itself subject to fewer negative headlines of late as fundraising started to improve and vacancies are filled.

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In a farewell email to DNC staff on Monday night, O’Connell thanked them and said she was proud of their work, while not offering a specific reason for her departure.

Perez quickly launched a search for a new CEO. O’Connell, who previously held a top job at the Democratic women's group Emily’s List, will help with the transition after she leaves next month.

Perez thanked O’Connell in the email for progress made under her watch. "When Jess walked in the door, the Democratic Party was broken," Perez wrote.

The CEO is the DNC's top staffer, overseeing day-to-day operations and political strategy at party headquarters, often while the chairman is away raising money, stumping for candidates and appearing in public.

"Rebuilding the party will take time. While it isn't an easy task, we developed a strategy, we implemented it, and we won races up and down the ballot in 2017," O’Connell said in a statement. "While I've made the decision to pass the baton, our work remains far from over and under Tom Perez's leadership and direction, our party will continue to build on the progress we've made in 2017."

Perez praised O'Connell for her help during his first year on the job, when the DNC was often defending itself from attacks while also trying to expand its mission to include year-round organizing.

"Jess O'Connell joined the DNC at a time when our party needed it the most," Perez said in a statement. "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. Jess laid the groundwork for an infrastructure to win in 2018, 2020 and beyond."

O'Connell had a senior role in Hillary Clinton's 2008 presidential campaign and was one of the campaign officials who urged the then-senator to fire an aide after a female employee lodged a harassment complaint, but was overruled by Clinton, according to recent reports in BuzzFeed and The New York Times.