WASHINGTON (AP) — President Joe Biden announced Jeff Zients on Friday as his next White House chief of staff, tapping an experienced technocrat who headed his administration’s response to the COVID-19 pandemic as Biden prepares for a reelection bid while facing an onslaught of investigations from a newly empowered House Republican majority.

Zients succeeds Ron Klain, a longtime fixture in Biden’s political orbit who led the White House through its highs — passage of consequential legislation like the massive infrastructure bill and the Democrats’ climate, health care and tax law, as well as dozens of judges confirmed in the first two years — as well as its lows, such as the rocky withdrawal of U.S. troops from Afghanistan. The transition is the first major personnel change for an administration that has had minimal turnover at its highest ranks and throughout the Cabinet.

“I’m confident that Jeff will continue Ron’s example of smart, steady leadership, as we continue to work hard every day for the people we were sent here to serve,” Biden said in a statement.

Zients, 56, will be tasked with shepherding White House operations at Biden’s pivotal two-year mark, when the Democratic administration shifts from ambitious legislating to implementing those policies and fending off Republican efforts to defang the achievements. Zients is also charged with steering the White House at a time when it is struggling to contain the fallout from discoveries of classified documents at Biden’s home in Wilmington, Delaware, and at his former institute in Washington, which has triggered a special counsel investigation.

Klain, in his resignation letter to Biden, said it was the “right time” for a transition.

“The halfway point of your first term – with two successful years behind us, and key decisions on the next two years ahead — is the right time for this team to have fresh leadership,” he wrote. “I have served longer than eight of the last nine Chiefs of Staff, and have given this job my all; now it is time for someone else to take it on.”

Zients, not known to be a political operative, is expected to focus on the task of governing as a separate circle of advisers take the lead on politics, such as senior adviser Anita Dunn and Jen O’Malley Dillon, a deputy chief of staff who managed Biden’s 2020 presidential campaign. Presidential counselor Steve Ricchetti, senior adviser Mike Donilon and deputy chief of staff Bruce Reed will continue in Biden’s inner circle, while Klain, a longtime Democratic operative, will continue to advise and be involved from the outside.

Through both the Obama and Biden administrations, Zients has been the go-to person for significant operational challenges — such as a nationwide coronavirus vaccination campaign — or to repair bureaucratic messes such as the glitches and crashes that marked the launch of HealthCare.gov in fall 2013.

Then-President Barack Obama also tapped Zients in 2009 to eliminate the backlog in applicants for the Cash for Clunkers program, which offered rebates to drivers who swapped old cars for fuel-efficient vehicles. Zients later took on a similar challenge to smooth sign-ups for an updated version of the GI Bill.

Zients was vice chairman of Biden’s transition after he won in November 2020 and served as director of the National Economic Council during the Obama administration and acting director of the Office of Management and Budget.

As COVID-19 coordinator, Zients led the effort that administered more than 220 million vaccinations in Biden’s first 100 days, while shoring up the nation’s supply of therapeutics and tests and distributing them. Zients gradually shifted the administration from a so-called “wartime” effort that grappled with COVID-19 at its most severe levels, to a strategy that would allow people to resume some normalcy with a virus that is likely to be endemic.

Although Zients left the administration in April 2022, he quietly returned in recent months to ensure the remaining two years of Biden’s term would be adequately staffed, a prelude to his taking on the much broader managerial role.