This Stanford Law grad was tapped in April to become newly installed Treasury Secretary Jack Lew’s right-hand man, just in time to help navigate the department rattling IRS scandal. Weideman earned the job by distinguishing himself as a go-to fixer for Tim Geithner, so he knows how to handle an emergency. Now he’s sweating longer-term challenges too: a comprehensive rewrite of the tax code, the ongoing budget battles with congressional Republicans, and international headaches from Europe to China. That’s a tall order.