Although this is not absolutely true in all cases, presidential approval ratings generally climb whenever something happens that is perceived by the majority of the American public as a serious threat to the United States or its interests. Political scientists attribute this to a “rally round the flag” effect.
Presidents have typically seen their popularity climb when foreign threats emerge. Both Presidents Bush are examples of this. The first President Bush saw his approval ratings climb in the lead-up to the Persian Gulf War and in its aftermath. The second President Bush became more popular in the days after the terrorist attacks of September 11, 2001.
The reason for this is that people tend to want strong leadership in dangerous situations. They want to feel as if they are being led by someone who will do what is needed to keep them safe. They also tend to want to present a united front to the world. They want to show that they are behind their country and its leaders in times of trouble.