This isn’t exactly an answer to the question, because I think it’s far-fetched that the US government could become either a communist or fascist regime.
However, one of the differences between communism and fascism is that, unlike the former, the latter does not depend on being imposed by a government. A communist is someone who advocates the establishment of a communist economic system, but until that day arrives, there is no communism.
But fascism is as much an underlying attitude as an overarching policy. It could be defined political bullying. If people are being attacked for lack of patriotism, then fascism is present. What happened to the Dixie Chicks was fascism (albeit relatively mild compared with what we know fascism to be capable of).
Fascistic policies can be implemented by a government piecemeal; a law against flag desecration would be an–again small–example of fascism for example. Socialism can be–and is-- implemented piecemeal too, but communism essentially rules out capitalism and regards the state as the primary source of employment, and that’s different.
Whether the Iraq war is fascism is debatable. If we’re sincere in wanting Iraq and the rest of the Middle East to be a better, more democratic place, then no. And self-defence is not fascism, but if we’re going around invading countries because there’s a small chance they might attack us, then yes. And if we were hopped up on a sense of militaristic vengeance in the wake of 9/11, then also yes.