John Podesta, the former White House chief of staff who led President Barack Obama’s transition team, is leaving his post as the head of the Center for American Progress, an organization official said today.

Podesta served as President Bill Clinton’s last chief of staff from 1998 to 2001, then founded CAP in 2003. The progressive think tank served as an unofficial Democratic policy headquarters during George W. Bush’s terms as president and became an ally of the Obama administration.

When Obama took office, CAP staff members flocked to the administration, including Gene Sperling, who became the director of the White House National Economic Council, and Gayle Smith, who became senior director at the National Security Council.

As CAP’s president and chief executive officer, Podesta became known as one of the most powerful Democrats in Washington outside the federal government.

He will serve as chairman of CAP’s board and will volunteer as an aide to Secretary of State Hillary Rodham Clinton once a week. The official said Podesta will focus “on longer-term strategic thinking for the institution across all issues.”

Podesta will be replaced by Neera Tanden, the chief operating officer at CAP and a former policy aide in the Obama and Clinton administrations. Tanden also sits on the board of directors of KnowYourCare/ProtectYourCare, a nonprofit organization dedicated to defending Obama’s health care law from Republican attacks.

A source on Tanden’s staff said the change had been in the works for months.

“He’s older, so [he] wanted to step back from day to day,” the source said.