Jeff Zients, who ran President Joe Biden’s Covid-19 response effort and served in high-ranking roles in the Obama administration, is expected to replace Ron Klain as the next White House chief of staff, according to three people briefed on the matter. Klain is expected to step down in the coming weeks.

The move to replace Klain is particularly important for Biden, who has entered a critical moment in his presidency and his political future. As he continues to weigh whether to seek reelection in 2024, the early stages of a special counsel investigation into his handling of classified documents has rattled Democrats and emboldened congressional Republicans, who now hold the House majority and have pledged their own probes.

Biden decided on Zients after an internal search when it became clear that Klain favored Zients as his successor, a factor that played a big role in the president’s decision. Klain had tapped Zients to lead a talent search for expected staff turnover following the midterm elections, but that didn’t ultimately materialize after Democrats performed better than expected. Klain is now the most significant departure and is being replaced by the person he picked to help bring in new team members.