By Ross Kerber Dec 16 (Reuters) - A new White House order aiming to rein in proxy advisory firms marks a major step in a broader Republican effort to weaken the role of investors and put more power in the hands of CEOs, corporate governance analysts and attorneys said. U.S. President Donald Trump told the U.S. Securities and ​Exchange Commission and other agencies last week to increase oversight of proxy advisers Institutional Shareholder Services and Glass, Lewis & Co, which help mutual fund companies a ...