Last summer, the United States was rocked by the first revelation to come from whistleblower Edward Snowden: Verizon (and likely other companies) routinely hands over millions of records on Americans' telephony metadata to the National Security Agency. Some in Congress have subsequently slammed the program, which is widely believed to collect such metadata on all Americans.

According to a new report by The Wall Street Journal, which cites anonymous sources, the NSA's telephony metadata program only "collects data for about 20 percent or less of that data, primarily because it doesn't cover records for most cellphones."

The Journal concluded that "[t]he dwindling coverage suggests the NSA's program is less pervasive than widely believed and also less useful."

If this revelation is borne out, it would undercut the White House's argument that the program is useful, legal, and effective.

Separately, The Washington Post spoke with anonymous intelligence officials who said that while collecting all metadata was ideal, so long as the metadata “is fairly spread across the different vendors in the geographic area that you’re covering,” that collection is useful.

“[Collecting 20 percent] is better than zero,” said NSA Deputy Director Rick Ledgett in an interview with the Post on Thursday, without describing the program’s exact scope. “If it’s zero, there’s no chance.”