The Federal Reserve chairman took his position this year facing plenty of economic factors that could stoke inflation, including: • Joblessness falling to multiyear lows, making it easier for workers to get a raise or a bonus, which could push up companies’ costs Then the Fed’s job got harder. Congress passed a large tax cut that will add a jolt of stimulus to an economy that no longer needs extra juice. The stock market loved it and kept zooming higher. But turbulence hit. On Feb. 5, the Dow Jones industrial average plummeted over 1,100 points, or 4.6 percent.