The one where it helped a little, they promise: Boston

What happened: Tamerlan and Dzhokhar Tsarnaev planted pressure cooker bombs along the finish line of the Boston Marathon on April 15 of this year.

What the government has said: In his testimony today — which was scheduled before last week's leaks — Mueller was asked about the FBI's failure to stop the attack. As we mentioned above, he indicated that the PATRIOT Act provision had helped, by identifying a person with unclear ties to the bombers and no apparent tie to the bombings.

Counterpoint: Tamerlan Tsarnaev was on the FBI's radar screen prior to the bombings. Despite that, the NSA and FBI's tools failed to identify and prevent the incipient plot. Mueller couldn't not mention the Boston attacks, since it was a large part of why he was on Capitol Hill. But it's hard to see how the death of Todashev is much of a victory for the government's surveillance tools.

Surveillance Matrix: No one appears to be claiming that the Boston bombings themselves were preventable, nor is a strong case being made that the law could have helped.

The ones they don't talk about: Underwear and shoe bombings, Fort Hood, and Times Square

What happened: In four separate incidents since 9/11, terror plots either failed or were executed without disruption. Those examples are the shoe bomber in December 2001, the Fort Hood shooting in November 2009, the underwear bomber that December, and the attempted Times Square bombing in May 2010.

What the government has said: In the context of the NSA revelations, nothing.

Counterpoint: It's not clear what could have been done in the Fort Hood incident, which bears more similarity to a mass killing by a deranged shooter than the other terror attacks. But in the other three cases, it was incompetence that interfered: Richard Reid's failure to take his shoe to the restroom before trying to light the fuse or the Times Square bomber's inability to construct a working bomb. Three of these incidents occurred within the timeframe during which the NSA's tools were in effect, yet, as in Boston, law enforcement did not intervene prior to the incidents.

Surveillance Matrix: Four different cases here. The shoe and underwear bombings were apparently preventable — but only through sheer, dumb luck. The Fort Hood shooting wasn't preventable, nor does it appear that the law played any role in stopping it. The Times Square bombing was prevented, again largely through luck, but the perpetrator may have been identified in part through phone records so we moved that one to the right.

The ones they can't talk about: the "dozens"

What happened: That is classified.

What the government has said: In his testimony before the Senate Appropriations Commitee onWednesday, NSA head Keith Alexander declared that the government had disrupted "dozens" of terror attacks in the United States and abroad thanks to the tools provided under the PATRIOT Act and the expansion of the Foreign Intelligence Surveillance Act. Alexander insisted that he couldn't talk specifically about those dozens of incidents, except, perhaps in a classified session with Congress. (Why these must be kept secret while the Zazi details weren't isn't clear.)