After months of consideration, Sen. Rand Paul, R-Ky., is moving closer to filing a lawsuit in federal court against National Security Agency surveillance programs.

A senior Paul staffer says U.S. District Court Judge Richard Leon's Monday decision that NSA opponents have standing to sue over the bulk collection of phone records makes Paul "much more likely" to file his own lawsuit.

The senior staffer, who spoke with U.S. News on background, says hundreds of thousands of people volunteered online as possible plaintiffs after Paul first floated the idea of a class-action lawsuit in June.

The senator has not firmly decided to file suit and it's still possible Paul will choose to instead assist with three already-filed lawsuits against the NSA.

If Paul does file a lawsuit it would be the fourth major legal attack against the NSA's bulk collection and five-year storage of American phone records.

Lawsuits against the phone-record collection are already filed in federal court by the American Civil Liberties Union in New York, by conservative legal activist Larry Klayman of Freedom Watch in Washington, D.C., and by the Electronic Frontier Foundation in San Francisco.

Klayman won a major victory against the NSA on Monday, with Leon ruling the phone record program is likely a violation of the Fourth Amendment. Leon granted a preliminary injunction barring the collection, but stayed implementation pending appeal.

Unlike the possible Paul lawsuit, Klayman only sought a handful of original plaintiffs. He is seeking for the "class" he represents to be defined by Leon to include all Americans affected by the program, which purportedly helps scuttle terrorist plots - an accomplishment Leon disputed.

The senior Paul staffer stressed that Paul is currently evaluating strategy options. If a lawsuit is filed, it would likely be in either D.C. or Kentucky. It's unclear which Paul-affiliated entity would file the challenge.

"As of now the senator is in the process of finding the best lawyer to file the [possible] suit [and] is still accepting more plaintiffs for the case," Paul spokeswoman Eleanor May said.

The website of Paul's political action committee, RANDPAC, currently has a pop-up advertisement that asks prospective plaintiffs to provide their name, email address and ZIP code. The ad says it seeks 10 million plaintiffs and asks for "a generous donation to help rally up to ten million Americans to support my lawsuit to stop Big Brother."

Regardless of the legal approach selected, the senior staffer said Paul's footwork to seek plaintiffs should help with possible standing issues, which have historically - although not in the initial Klayman case decision - derailed anti-surveillance lawsuits.

The pending EFF and ACLU lawsuits also do not have a large number of individuals named as plaintiffs. The EFF lawsuit is brought by a coalition of advocacy groups and the ACLU's challenge is brought by the organization itself, as a customer of Verizon Business Network Services, the entity specified in an officially recognized court order leaked by Edward Snowden.

Although Judge Leon took a preliminary sledgehammer to the Justice Department's legal argument and U.S. District Court Judge William Pauley of New York is also considering an injunction request from the ACLU, the Paul staffer stressed the legal fight may take a while to resolve and said the senator wouldn't be too late to have a meaningful impact.

In the sweeping Monday victory for NSA critics, Leon ruled Klayman had standing to challenge the phone record collection, that his court had the authority to review Foreign Intelligence Surveillance Court actions, that the landmark 1979 case Smith v. Maryland was ill-suited to justify the surveillance and that the program likely violates the Fourth Amendment.

Leon described the collection as "almost-Orwellian" and said "the government does not cite a single instance in which analysis of the NSA's bulk metadata collection actually stopped an imminent attack, or otherwise aided the government in achieving any objective that was time-sensitive."

Paul, who has introduced legislation to ease standing issues and also to forbid indiscriminate collection of Americans' records, applauded Leon's decision Monday.

"I will continue to fight against the violations of Americans' constitutional rights through illegal phone surveillance until it is stopped once and for all," he said in a release.

In addition to considering a lawsuit against the phone record collection, Paul is also looking at legal options against NSA Internet programs. Klayman is currently suing to halt the PRISM Internet program, but Leon did not grant an injunction in that case.