Actually, there's a lot he can do. Congress controls the purse, not the president and definitely not some unelected billionaire. I know with the current Senate, the chances of a conviction are slim to none, BUT he can keep speaking out, he can help pass laws to limit the executive's power and more. Heck, congress can take back control from several executive departments, if they wish. There have to be enough Republicans who know how dangerous Trump is and actually support the constitution to get some things DONE.