In the example I was using (sorry for going crazy and spanning it across 2 posts...), I was talking about the possibility of a president who changes the keywords that they are searching for from "Al Queda" to "<his name> sucks", then having anybody who says that silently rounded up and killed.
Now, for the first part: it's been shown that the president (or somebody close, whatever) can order wiretaps on people if they suspect they are a threat to the country (currently, terrorists). What if you had a president who decided that anybody who doesn't like him is a threat to the country? Because there's no court order involved, he can get the wiretaps for it.
For the second part, as you said, he has a lot of power. I'm sure it would be possible to pull it off. Or, if anything, have them arrested, tried, and hanged for being a traitor. If they use propoganda properly (like with terrorists), people will think that the people being hanged are scum, non-human, etc. and won't care. But that's neither here nor there.
So what worries me about the wiretaps is that it's giving the president (not just the current one, ANY president) the excuse to remove freedom of speech/invoke 1984-style "thought police."