When we use the term "United States," it's usually identifying something dealing with official, govermental, business side of the nation. The solid mechanics of the country. The United States Senate. The United States Postal Service. The President of the United States.
"America," however, is used for the ideals, the individual apsects of the nation. The abstract ideas of the country. The American dream. The American flag. America, the Beautiful.
Semantics have power, and they exist for a reason. The United States is a system. America is an idealistic dream of the people living there.
When a country is hit hard by crisis, war, disease and terror, these two become very closely united. Some would call it patriotism. Yet, I think at at time like this, more than ever, the two should not be confused. Neither should extend to overtake the other. Your government is not your nationality. Dreams are more than the physical mechanisms behind them.
Germany was not the Nazi Party of Germany, but was swept up by it in the end. People need to know there's a difference between support and submission. To be an American, it is your right and privilege, and some might even say patriotic duty, to watch the United States closely.