He’ll reunite with ex-boss and former Treasury Secretary Timothy Geithner, now Warburg’s president. : NEW YORK: Jake Siewert is leaving Goldman Sachs to join New York-based private equity firm Warburg Pincus. The Clinton and Obama administration alum is rejoining former boss Timothy Geithner, who joined Warburg Pincus as president in 2014, at the firm. Siewert worked at Goldman for more than nine years as its top communications executive. From 2009 to 2011, he was counselor to Geithner, then Treasury secretary. Previously in the public sector, Siewert was President Bill Clinton’s press secretary.