From today’s NYT

Mr. Obama has kept up pressure on the Senate to pass the legislation by arguing that the surveillance it authorizes is vital to thwarting a terrorist attack, despite a lack of evidence that it has ever done so.

In a statement issued shortly before Mr. Obama spoke, James R. Clapper Jr., the director of national intelligence, said that intelligence professionals “will lose important capabilities” if the authorities expire.

Senior administration officials say that even if the programs cannot be shown to have foiled any attacks, they provide essential “building blocks” on which terrorism investigations are built, akin to grand juries, which are an integral part of criminal cases even if they never themselves stop a crime.

Emphases added. So much for evidence-based policy-making.