We could also call this the “Appeal to Patriotism.” Whether or not a person is sufficiently “patriotic” can be a life or death point in political matters, particularly in nations like the United States where national self-awareness has reached in incredible degree.
Flag-waving is an attempt to win support for one’s position by showing either that a particular person or action is patriotic or that supporting a policy will benefit the nation. It also works in the opposite direction: If you can prove to Americans that an action is unpatriotic, then you’ve all but handed it a death sentence. How often do we hear the accusation that such-and-such a person “hates America,” in attempts to attach negative associations to that person.
As the name “flag-waving” implies, this technique is usually attached to symbols, such as the American flag or the Statue of Liberty or some other universally recognized image. A politician who appears in a photo with a flag wrapped around his shoulders, or with a flag blowing in the background, this is an attempt to cause the viewer to take all the positive feeling associated with the flag and then, consciously or unconsciously, apply them to the person, even if they may have no rational cause for making such an association.