The National Security Agency’s huge snooping on Verizon phone records may be legal, but is the practice effective in fighting  terrorism?

Since the program was top secret until Wednesday night, when The Guardian’s Glenn Greenwald broke the NSA Verizon phone records story, it’s difficult to determine what kind of impact such a vast store of information has in rooting out terrorists.

But if you go by experience, this type of surveillance doesn’t have a great track record, says Julian Sanchez, research fellow at the Cato Institute, a libertarian think tank.

Of the effectiveness of the Verizon (NYSE:VZ) data collection, which includes the duration of phone calls and the numbers involved, but not actually listening in on the calls, “it’s hard to say," according to Sanchez. 

“Of course, they claim that it is,” Sanchez said, referring to the government, whether it be the  administration of President Obama or that of his predecessor, George W. Bush. “The trouble is that those claims keep turning out to be false.”

Sanchez, who researches privacy and civil liberty issues, said Americans have reasons to be skeptical, pointing out that analyzing phone records leads to too many false findings.

“We just shouldn’t take their word for it,” he said of the government touting the efficacy of such analysis.

Under Bush, the NSA was illegally wiretapping American citizens’ phones without warrants, a much bigger scandal than what The Guardian exposed Wednesday. At the time, Bush defended the program, saying it saved American lives.

The warrantless wiretapping also generated false leads in the war on terror and misidentified some American citizens as terrorists because NSA analysts found connections when there were none, Sanchez said.

“It was difficult to point to any clear-cut cases that the program … disrupted a terrorist plot,” he stated.

Analysis of phone records is used in conjunction with other methods to identify terrorist suspects and attempt to thwart terrorist plots, which makes it hard to discern whether a particular tactic is to be credited for apprehending a certain person or foiling any specific attack.

But as with the Bush administration, Obama's is trumpeting the usefulness of the NSA collecting phone records. The White House also has the top two lawmakers on the Senate and House intelligence committees defending the program.

Sen. Saxby Chambliss, R-Ga., the vice chairman of the Senate Intelligence Committee, vouched for the effectiveness of the data collection in the war on terror.

“It has proved meritorious because we have gathered significant information on bad guys, but only on bad guys, over the years,” he said at an impromptu news conference Wednesday.

In a joint statement, the leading lawmakers on the House Intelligence Committee, asserted that the program, conducted under the Foreign Intelligence Surveillance Act, thwarted at least one attempt to attack America.

“Importantly, these activities have led to the successful detection and disruption of at least one terrorist plot on American soil, possibly saving American lives,” said Chairman Mike Rogers, R-Ala., and ranking Democratic member Dutch Ruppersberger, D-Md., in the statement, which explained how the program didn’t involve eavesdropping on phone calls.

Sanchez noted that while phone records may have been useful in individual terrorism cases, it is flawed logic to say that means seizing everyone’s records would be helpful to the government’s counter-terrorism efforts.

“That is not the same thing as saying it’s necessary to obtain everyone’s phone records,” he said.