The single most striking deterioration that has happened in the United States in the last ten years or so is the loss of the right to dissent. The United States government has always done terrible things, but through it all Americans have always had the right to complain about it. The reason that we still hear a lot about what happened in Chicago in 1968 is that it was such an aberration (if you haven't seen it, you should watch the movie 'Medium Cool' some day). Kent State was another aberration, but I wouldn't be surprised, the way things are going, to see another such incident before the end of Bush's Presidency.
The consistency of support amongst all political groups for freedom of assembly and freedom of speech has been the best thing about the United States, and it is now dead or dying. The old strain of American libertarianism, which was perceived as flowing directly from the spirit of the American Revolution, and which always supported free speech, now only exists in the form of opposition to any control over gun ownership.
Over and over again we are now seeing people arrested for holding up signs, wearing t-shirts with the 'wrong' (i. e., non-Republican Party) message on them (with arrest clearly being used solely as a method of removing the ability to make a public point), or even standing in the wrong place. Freedom of assembly no longer exists, with all manner of artificial and unnecessary restrictions which make assembly useless. Even stronger restrictions are planned. Since there is no real outlet for any contrary opinions in the controlled media, only one voice, the official talking points of the Republican Party (and the Democrats who shamelessly follow them), is allowed.
This moral deterioration has occurred in American conservatism. Conservatives who used to be staunch supporters of freedom of speech now see the only issue as maintaining power in their Republican Party, and they applaud any efforts to prevent any contrary point of view from being presented. Conservatives always saw themselves as the true defenders of the values of the American Republic. Their moral deterioration into admit-no-dissent partisanship appears to be permanent, and is why the United States is doomed. American economic superiority is also eventually doomed, as it rested on the freedom of thought required for science and technology, and the Republican attack on science continues and is accelerating. People in countries all over the world who used to look to the United States as an unattainable model of freedom are now able to protest, and do, but protest of any kind is no longer allowed in the former home of freedom.