Robert D. Kaplan writes in the Atlantic about private military contractors like Blackwater. He points out that these private concerns have been a part of America's military operations since the early Cold War, that they provide numerous essential services more cheaply and efficiently than the military could, that the personnel hired by these firms (mostly retired US military) are of uniformly high quality, that they provide humanitarian as well as military services, and (interestingly) it was Bill Clinton, not George Bush, who forged the close relationship between the U.S. military and former Halliburton subsidiary Kellogg, Brown and Root, a relationship that carried over from Bosnia/Kosovo to Afghanistan and Iraq.
Bottom line: These companies will be an essential and growing part of future American military actions no matter who is in the White House; they save the taxpayers a lot of money; and because they are so important in so many areas, Congress has to set clear guidelines on how they are to be employed.