In my view, Kmiec is plainly right that nothing in Comey's testimony suggests anything like another Watergate. Consider how little we know about the facts. We don't know what the program was that Comey and Ashcroft wouldn't authorize, or why they wouldn't authorize it. And as far as I can tell, there is absolutely no evidence whatsoever that the President intentionally violated a known legal duty or participated in some kind of cover-up. (Note that when Comey met with the President one-on-one, according to his testimony, the President backed him.)
At the same time, the test for whether the Comey story deserves attention surely can't be whether it's as bad as Watergate. I'm sure there's room in there for political news that doesn't quite hit Watergate break-in and Nixonian cover-up levels. And just as we don't know the facts to make the Watergate comparison stick, we also don't know the facts to suggest, as Kmiec does, that this was just some sort of routine disagreement within the Executive branch. We do know that there was something going on that led the Attorney General, Deputy Attorney General, FBI director, Head of OLC, and some of their leading staffers — which, we have reason to believe, was everyone in DOJ and the FBI who actually knew of the facts of what was happening — to be ready to resign. Kmiec doesn't know what it was, and neither do we, but it seems odd to imagine it must not have been over something very important.
Oh, and on the technical questions in Marty's post, Marty seems right to me — in particular, I think he's very likely right that the point of the AG's signature was to persuade the telecom companies to go along. I assume the lawyers for the ISPs and telcos insisted on some sort of legal process to give the government access to their networks, and the 45-day authorizations signed by the President and the AG were the process that the telcos and ISPs accepted.