The correct answer is D) politics and public opinion.
What is generally considered to be the greatest source of influence on the president of the United States is politics and public opinion.
This statement is commonly perceived to be correct because the President of the United States is always paying close attention to what mass media and people say about him, his decisions, and his programs. The President of the United States knows that his public image and the citizen's perception of his government is vital if he wants to go for reelection.