When he is right and when he has public opinion behind him — and those two conditions are practically synonymous — the President of the United States is within his own realm the most influential person in the world, and no man or group of men can undermine his words.
In the power that the president exercises, there are two elements. There is his demeanor, his moral judgment and his resolve to triumph in the name of truth, justice and American values. There is also the collective influence of the American people with their devotion to principle and fair play. When these two elements of strength combine toward a common goal, then and only then does the president have the influence needed to best serve the United States at home and abroad, which is what Americans expect from their president in the first place.
Presidential influence comes at a cost: The president promises to lead well with reasonable policies, and the public promises to support the president when he or she does. Considering that the 2016 presidential candidates are the devious insider Hillary Clinton and the narcissistic charlatan Donald Trump, whether the promises made by the next president and by the public will be kept or broken is more uncertain than usual.