An aging workforce and low productivity growth will keep the United States from growing faster than about 2 percent annually on a sustainable basis, Williams said at the Bay Area Economic Institute's annual forecast conference. Donald Trump, sworn in as the 45th U.S. president just hours earlier, has promised his economic policies will boost growth to 4 percent. It was unclear how that ambition will square with the Fed's determination, as articulated by Fed Chair Janet Yellen earlier this week, to raise rates gradually in order to prevent the economy from overheating.