I saw the Moyers piece, and I agree with you that it was excellent. I am also alarmed about the problem of executive overreach, and Fein and Nichols make a good case for impeachment's importance in reigning in future presidents.
The other side of this tragic turn of events is Congressional enabling, which Moyers discusses as well. What's their responsibility, do you think? Almost all of the overreach has been with the full support, or more recently grudging acquiescence, of the legislative branch. It seems slightly unreasonable to expect people to curtail their own authority, especially people with the megalomaniacal tendencies required to run for president -- that's why the Founders gave the various branches the authority to reign each other in. Congress could redress their own Constitutional lapse by throwing down the impeachment gauntlet, but maybe they should also start doing their own jobs!
There is an interesting op-ed in the New York Times that talks about executive overreach in the area of war making, and how the Congress is still being shy about standing up for its own Constitutional power.