For the first time, a public court has determined that the National Security Agency's collection of metadata on Americans' phone calls probably violates the Constitution and should be stopped.

That's the short version of a ruling on the NSA's bulk collection of phone records released by the D.C. District Court on Monday. The injunction ruling determined that the plaintiffs had standing to file a lawsuit — in other words, that they were affected by the NSA's data collection — and that a court would likely find that the collection violated the Fourth Amendment of the Constitution. Given that the plaintiffs suffered "irreparable harm" from the data collection, the court determined that the data collection should be halted — though that order was withheld, pending appeal.

The decision, responding to a lawsuit initiated by Larry Klayman, the founder of Judicial Watch, was written by U.S. District Court Judge Richard Leon, a George W. Bush appointee. The lawsuit is a direct result of the leaks from Edward Snowden, the first of which came out one day before the suit was filed.

Leon doesn't mince words in his critique, suggesting that the technology involved renders past judicial determinations inapplicable. The NSA gathers on-going data on phone calls placed and their length, the sort of thing that once needed to be done on a line-by-line basis.

"[T]he almost-Orwellian technology that enables the Government to store and analyze the phone metadata of every telephone user in the United States," Leon writes, "is unlike anything that could have been conceived in 1979," when the Supreme Court case of Smith v. Maryland first allowed the government to collect such data. "The notion that the Government could collect similar data on hundreds of millions of people and retain that data for a five-year period, updating it with new data every day in perpetuity, was at best, in 1979, the stuff of science fiction."

"When do present-day circumstances ... become so thoroughly unlike those considered by the Supreme Court thirty-four years ago," he asks, "that a precedent like Smith simply does not apply? The answer, unfortunately for the Government, is now."

What Leon found most important in rejecting the argument, however, was precisely that the use of phones had evolved significantly in the past decade.

It is now safe to assume that the vast majority of people reading this opinion have at least one cell phone within arm's reach. … In fact, some undoubtedly will be reading this opinion on their cell phones. … Cell phones have also morphed into multi-purpose devices. They are now maps and music players. They are cameras. They are even lighters that people hold up at rock concerts. … Count the phones at the bus stop, in a restaurant, or around the table at a work meeting or any given occasion. Thirty-four years ago, none of those phones would have been there.

"The ubiquity of phones," Leon continues, "has dramatically altered the quantity of information that is now available and, more importantly, what that information can tell the Government about people's lives." Metadata can now "reveal an entire mosaic — a vibrant and constantly updating picture of the person's life."

The issue of standing Leon addresses in his ruling has long been one of the stumbling blocks for those looking to call the NSA's activity into question. In February — before the leaks from Edward Snowden that are directly cited as the inspiration for this lawsuit — the Supreme Court threw out a challenge to the NSA's warrantless wiretapping program because the ACLU and other plaintiffs couldn't prove they'd been affected by it. The Snowden leaks made obvious that every American has had his or her phone metadata collected.

Monday's ruling — even though its judgment is stayed pending an appeal — will provide ammunition to those who've sought to eliminate the NSA's ability to collect phone metadata. There are multiple bills before Congress right now that would refine the Patriot Act's Section 215 to eliminate the ability to collect this information; President Obama's own panel recommending reforms will apparently offer some restrictions on the practice. Update, 3:00 p.m.: In a statement, Sen. Mark Udall says the ruling "only underscores the urgent need for Congress to act."

In other words, the program, already faltering, may have just received its death blow.

Update: 4:00 p.m.: In a statement to Glenn Greenwald (and reported by The Times) Snowden weighs in.

I acted on my belief that the N.S.A.'s mass surveillance programs would not withstand a constitutional challenge, and that the American public deserved a chance to see these issues determined by open courts. Today, a secret program authorized by a secret court was, when exposed to the light of day, found to violate Americans’ rights. It is the first of many.

Hat-tip: Carrie Johnson via Julian Sanchez.