Since that letter, I have learned more. The American Civil Liberties Union sent a letter to all senators on May 6, noting that in the view of the Senate Intelligence Committee chairwoman, Dianne Feinstein, “there are at least eleven OLC opinions on the targeted killing or drone program.”
I joined the ACLU a couple years ago in part because I'd read a lot about the various illegal and immoral activities parts of the government has done and didn't see an obvious way for me, a somewhat normal, random guy, to do much about it. There's a lot of (justified) Internet outrage over the murder of Anwar al-Awlaki, widespread spying, and so forth. But without converting outrage to action, the outrage means very little.
Does my $50 do much on its own? Perhaps not. But it means something.