Noam, for what it's worth: I don't have exact quotes but when the letter came up in yesterday's conference call, Clinton spokesman Phil Singer seemed to imply that the campaign had not coordinated or officially signed off on it. I believe he said they'd gotten "a heads-up." Now, there may well be more to it than that. But it's at least possible that those donors acted mostly or entirely on their own--perhaps to give Hillary plausible deniability if confronted with a backlash.
--Michael Crowley