(CNN) Joe Biden has hired Jen O'Malley Dillon as his new campaign manager in a shake-up of top-level staff as the former vice president looks to close out the Democratic primary against Vermont Sen. Bernie Sanders and prepare for the general election.

O'Malley Dillon, a former top Barack Obama campaign aide who last year managed Beto O'Rourke's presidential bid, had been helping Biden's campaign since the Nevada caucuses, where Biden began his rebound after disappointing showings in Iowa and New Hampshire.

She replaces Greg Schultz, who is remaining with the campaign in what's being described as an important role that hasn't fully been defined.

Anita Dunn, who Biden had elevated above Schultz and was handed final decision-making authority on the campaign weeks ago, will remain on as a senior adviser.

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