After nearly six years presiding over the National Security Agency's dragnet collection of U.S. phone records, President Barack Obama is readying his pen to sign legislation ending that program.

But passage of the White House-supported USA Freedom Act – up for a cloture vote Tuesday in the Senate, following House passage of a different version in May – may have one major downside for mass surveillance foes, aside from what some critics deem limp-wristed reforms.

Legal experts say passage of the bill, which would end the automatic bulk collection and in-house retention of phone records, may short-circuit lawsuits that claim the collection is illegal. That would deprive citizens not only the satisfaction of possible rulings that Obama and President George W. Bush ordered violations of their constitutional rights, but also head off Supreme Court review of a 35-year-old precedent the government says allows it to collect huge amounts of data provided by ordinary Americans to businesses.

Three federal courts of appeal are weighing challenges to the NSA phone record program and other lawsuits are pending in district courts, alleging constitutional violations and that the program exceeds the authority granted by Section 215 of the Patriot Act.

Thus far, one federal judge has ruled against the program, saying it “almost certainly” violates Fourth Amendment rights. The Supreme Court is expected to have the last word – should legislation not prevail first. The high court likely would decide if the 1979 Smith v. Maryland decision – which found a suspect had no expectation of privacy over metadata provided to a third party – actually allows for the bulk collection.

Douglas Laycock of the University of Virginia School of Law says legislation ending the collection almost certainly would kill the lawsuits.

“The plaintiffs may try to keep the cases alive by arguing that the statute doesn’t do the job, or that the statute doesn’t reach some of what they say is unconstitutional,” Laycock says. “But to the extent that they cover the same things, the lawsuits will be moot.”

He adds: “It’s pretty inconceivable that the Supreme Court would hear one of these cases after a statute makes them moot.”

Martin Redish, a professor at the Northwestern University School of Law, agrees. The plaintiffs would stand a better chance of surviving mootness claims if Obama voluntarily ended the program, but legislation doing so likely shuts the door, he says.

“Usually, when the cessation of the challenged conduct is brought about by formal governmental action, that takes the case out of the ‘capable of repetition yet evading review’ category,” Redish says.

Attorney Luke Malek, working on Idaho nurse Anna Smith’s challenge to the program, which goes before a panel of the U.S. Court of Appeals for the Ninth Circuit on Dec. 8, recognizes the threat.

“We all have mixed feelings about this,” says Malek, also a Republican state lawmaker in Idaho. “While a change of law would protect citizens more immediately, prevailing with a lawsuit would leave an indelible constitutional precedent to prevent future government attempts to surveil innocent Americans.”

Possible avenues to keep the suits alive if the Freedom Act becomes law include asking for damages or seeking the deletion of records plaintiffs can prove were taken, says Harvard Law School professor Richard Fallon.

If lawsuits against the phone record collection merely seek an injunction against future collection and a declaration the collection was illegal, they likely would be moot, he says.

Legal activist Larry Klayman's two lawsuits against the program seek damages, as do two lawsuits filed by the Electronic Frontier Foundation. Lawsuits on appeal by the American Civil Liberties Union and Smith do not, nor does a stalled suit brought by Sen. Rand Paul, R-Ky.

Electronic Frontier Foundation Legal Director Cindy Cohn says the Freedom Act may hamper the lawsuits, but would not end the fight.

“If the USA Freedom Act passes as currently written there is a distinct possibility that it could limit our ability to get injunctive or ongoing relief in the telephone records cases, since, if implemented in good faith, the mass collection we complained about would no longer be occurring,” she says.

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But Cohn says plaintiffs in the foundation's cases would “still have claims for past collections and to require the government to destroy what they have collected so far” and would be able to bring new court challenges or amend existing lawsuits if they learn the government continues bulk collection.

Klayman, who won in December the first, and thus far only, district court ruling against the program, which he defended on appeal this month, plans to vigorously object to potential government claims his lawsuits are moot.

Klayman says the requests for damages will keep his cases against the program – one on appeal, and a larger class-action on hold in district court – on track. He also plans to argue the NSA and government officials are not to be believed if they claim bulk collection of phone records has ended.

Klayman’s lawsuits cite the 1971 Supreme Court decision Bivens v. Six Unknown Named Agents as allowing damages against individual officials. He's seeking billions of dollars, but Laycock and Redish doubt the effort will succeed and say if the requests for damages fail, courts would not need to address the underlying questions about the program's legality.

Redish says the Supreme Court “has put so many restrictions on Bivens actions that it hardly ever works regardless of mootness.”

Laycock says under Bivens “officials have official immunity unless the law was clearly settled that collecting these records was illegal; [And] clearly the law was not settled.”

Klayman pushes back on that analysis.

“It would be the clearest cut Bivens case in the history of the world, violating constitutional rights by this magnitude,” he says. “We have an absolute right to those damages. … they knew or had reason to know they were breaking the law.”

If officials did not believe they were breaking the law, their conduct was reckless or grossly negligent, he says.