In the biggest legal blow to the National Security Agency since the dragnet spying scandal broke in June, a federal judge ruled Monday that the U.S. government "almost certainly" violated the constitution by mass collecting data on nearly every single phone call within or to the United States.

“Today, a secret program authorized by a secret court was, when exposed to the light of day, found to violate Americans’ rights," declared NSA whistleblower Edward Snowden in a statement on the ruling released by journalist Glenn Greenwald Monday afternoon. "It is the first of many."

"This is a vindication for our fellow citizen Edward Snowden who came forward because he believed the government was violating our constitutional rights." –Glenn Greenwald, journalist

In a 68-page statement released Monday, U.S. District Court Judge Richard Leon issued stinging criticisms of NSA metadata snooping, declaring, “I cannot imagine a more ‘indiscriminate’ and ‘arbitrary invasion’ than this systematic and high-tech collection and retention of personal data on virtually every single citizen for purposes of querying it and analyzing it without judicial approval."

Leon, who was appointed by former President George W. Bush, ruled in response to a lawsuit brought by conservative activist Larry Klayman that phone metadata collection violates Fourth Amendment protections against unlawful searches and seizures without demonstrating any role in preventing "terrorist" attacks.

Leon granted Klayman's demand for a temporary injunction on the grounds that the lawsuit was likely to win. Yet, he did not immediately implement his ruling, pending a government appeal.

Nonetheless, Leon's opinion is being widely lauded as "the first significant legal setback for the NSA’s surveillance program since it was disclosed in June," as Josh Gerstein writes for Politico.

Because it takes aim at a 1979 Supreme Court ruling that the Obama administration says justifies the NSA secret spying, Leon's legal argument could have far-reaching consequences. "If upheld on appeal, the judge's reasoning could force the spy agency to reconsider other domestic spying programs that involve warrantless collection of "metadata" about Americans' communication," writes Andrea Peterson for The Washington Post.

The ruling is certain to "influence other federal courts hearing similar arguments from the American Civil Liberties Union," write Spencer Ackerman and Dan Roberts in The Guardian.

“This is a strongly worded and carefully reasoned decision that ultimately concludes, absolutely correctly, that the NSA’s call-tracking program can’t be squared with the Constitution," declared ACLU Deputy Legal Director Jameel Jaffer in a statement emailed to Common Dreams. "We hope that Judge Leon’s thoughtful ruling will inform the larger conversation about the proper scope of government surveillance powers, especially the debate in Congress about the reforms necessary to bring the NSA’s surveillance activities back in line with the Constitution."

Snowden and his supporters say the ruling underscores the vital importance of Snowden's revelations.

“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,” said Snowden.

"This [ruling] is a vindication of the constitutional rights of American citizens, who had intimate information collected about us without our consent," said Glenn Greenwald on a Monday MSNBC interview about Leon's ruling.

He added, "This is a vindication for our fellow citizen Edward Snowden who came forward because he believed the government was violating our constitutional rights."

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