Paul, a libertarian-leaning Kentucky Republican and potential presidential contender, inveighed against NSA surveillance and promised a “historic” lawsuit. He and his allies hope to take the case, which focuses on the NSA’s gathering of telephone metadata, to the Supreme Court.

“There’s a huge and growing swell of protest in this country of people who are outraged that their records are being taken without suspicion, without a judge’s warrant and without individualization,” Paul said at a news conference outside the U.S. District Court for the District of Columbia.

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Ken Cuccinelli, Virginia’s former attorney general and last fall’s unsuccessful GOP nominee for governor, is serving as lead counsel for the case. Paul was also joined by Matt Kibbe, the president and CEO of the tea party-tied group FreedomWorks. The men stressed they wanted to make sure the NSA was not going beyond the boundaries of the Constitution.

“I’m not against the NSA, I’m not against spying, I’m not against looking at phone records,” Paul said. “I just want you to go to a judge, have an individual’s name and [get] a warrant. That’s what the Fourth Amendment says.”

The senator also argued that there’s “no evidence” that NSA surveillance of phone data has stopped terrorism, even as the agency’s proponents say it plays an important role in keeping the country safe.

Reports over the weekend indicated that the NSA takes information only from 20 percent of American calls, or less — a lower figure than previously thought.

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“Whether you breach the Fourth Amendment 20 percent of the time or 100 percent of the time, it’s still not the point,” Paul told POLITICO in an interview Saturday. “The point is whether or not you still collect millions of people’s information with a single warrant.”

In response to the lawsuit, a spokesman for the Justice Department said Wednesday: “We remain confident that the Section 215 telephone metadata program is legal, as at least 15 judges have previously found.”

Paul has been publicly promoting the lawsuit for weeks — an effort that appears to also be helping him build a campaign infrastructure for 2016, when he’s up for reelection to the Senate and when the White House is in play.

He initially directed potential class-action signatories to websites including RandPAC.com and to his Facebook page, which sent visitors to RandPaul2016.com. Signing up on both sites also added visitors to his campaign’s email lists. Now the senator also is pushing Defendthe4th.com, a reference to the Fourth Amendment. The Paul campaign arm will still be able to access those email lists, an adviser to the senator confirmed. They are working in conjunction with the FreedomWorks-backed initiative ConstitutionDefenseFund.com.

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“Any money donated through the petition page on www.ConstitutionDefenseFund.com will be going towards the legal costs of this suit,” FreedomWorks spokeswoman Jacqueline Bodnar confirmed after the event in an email. “We expect this case to go all the way to the Supreme Court, so it’s going to be expensive.”

The lawsuit joins one of several that are already in the court system targeting the NSA. When asked how their case would differ, Cuccinelli stressed the class action aspect.

“This case is, first of all, the only case that is strictly challenging the Fourth Amendment elements of the telephone metadata gathering,” Cuccinelli said. “Second of all, this will be certified later in the case as a class action, on behalf of all Americans. The other cases thus far are on behalf of individual plaintiffs … that does not provide relief for every American using telephones. This case will.”

Larry Klayman, the plaintiff in one of the cases already in the court system, said in a statement, “Imitation is the sincerest form of flattery. We are pleased that Senator Paul has finally taken up the fight and I trust that we can work together to protect the constitutional rights of all Americans.”

The American Civil Liberties Union, at the center of another NSA case, offered, “We agree that the NSA’s phone-records program is unconstitutional … We’ve advanced these arguments in our own lawsuit against the NSA, and over the next few weeks we’ll make them to a federal appeals court.”

The “plaintiffs” in Paul’s case speak “on behalf of themselves and all others similarly situated … who are or have been customers, users or subscribers of phone service in the United States since 2006,” according to an early look at the complaint shared with POLITICO’s Playbook.

The suit challenges President Barack Obama, Director of National Intelligence James Clapper, NSA Director Keith Alexander and FBI Director James Comey. It blasts “Defendants’ mass, suspicionless, non-particularized collection, storage, retention, and search of telephone metadata related to every domestic or international phone call made or received by Plaintiffs and class members.”