WASHINGTON -- The National Security Agency has told Sen. Bernie Sanders (I-Vt.) that it can not answer his question about whether it collects information on members of Congress because doing so would violate the law.

In a letter to Sanders, which was obtained by The Huffington Post, Gen. Keith Alexander, who heads the agency, insisted that nothing the NSA "does can fairly be characterized as 'spying on Members of Congress or American elected officials.'" But Alexander wouldn't go more in depth than that, arguing that he would be violating the civilian protections of the program if he did.

"Among those protections is the condition that NSA can query the metadata only based on phone numbers reasonably suspected to be associated with specific foreign terrorist groups," Alexander wrote. "For that reason, NSA cannot lawfully search to determine if any records NSA has received under the program have included metadata of the phone calls of any member of Congress, other American elected officials, or any other American without the predicate."

READ THE FULL RESPONSE HERE:

A request for comment from Sanders' office was not immediately returned, though the senator acknowledged to The Huffington Post on Tuesday that he had received the letter. Undoubtedly, he and others will view the response as a lawyerly punt.

Sanders had written Alexander in early January to ask if the NSA has or is currently spying "on members of Congress or other American elected officials." The letter went on to define spying as including "gathering metadata on calls made from official or personal phones, content from websites visited or emails sent, or collecting any other data from a third party not made available to the general public in the regular course of business.”

The NSA, for its part, maintains that collecting metadata on phone calls doesn't rise to the level of "spying."

Alexander doesn't actually say so in his letter, but it's very possible that the NSA collects data on members of Congress just as it does on everyone else, in bulk. The NSA said in a statement earlier this month that members of Congress have the "same privacy protections" as ordinary citizens, which means that they too might be caught up in the NSA's terrorism queries of its telephone database, which may sweep up millions of innocent people in a single search.

UPDATE: 7:15 p.m. -- Sanders, who has introduced legislation to bar the wholesale collection of phone records without a warrant, responded to the NSA on Tuesday evening. In addition to noting that the agency didn't deny collecting data on Congress, he warned of potential abuses.