Paul remains steadfast against NSA collection of data. (Jim Cole/AP)

This post has been updated.

In the wake of a federal appeals court ruling Thursday that the National Security Agency's collection of million of Americans' phone records violates the Patriot Act, declared and potential 2016 candidates reactions were decidedly mixed.

Sen. Rand Paul (R-Ky.) effusively lauded the court's ruling, as did Sen. Bernie Sanders (I-Vt.), who is seeking the Democratic nomination. Sen. Ted Cruz (R-Texas) was a bit more measured, while Sen. Marco Rubio (R-Fla.) defended it from the Senate floor. The others have so far remained silent.

In a speech Thursday, Rubio defended the collection of data, saying that the perception that the government is continually listening to the calls and thumbing through the credit card bills of people is "absolutely, categorically false." He said there have been no documented abuses of the system and that the threat against the U.S. is not theoretical.

"One day, I hope that I’m wrong, but one day there will be an attack that’s successful," Rubio said. "And the first question out of everyone’s mouth is going to be, why didn’t we know about it? And the answer better not be because this Congress failed to authorize a program that might have helped us know about it."

For Paul, the court ruling is a victory in a battle he has been fighting in the Senate, courts and now on the campaign trail.

In the months leading up to his presidential announcement, Paul has seemingly shifted positions on everything from defense spending to foreign policy. But he has been steadfast on one issue: vehemently opposing surveillance and the bulk collection of phone records by the NSA.

Paul lavished praise on Thursday's ruling, declaring it a "monumental decision for all lovers of liberty" and commended the court for upholding the Constitution and protecting Fourth Amendment rights.

"While this is a step in the right direction, it is now up to the Supreme Court to strike down the NSA's illegal spying program," Paul said in a statement.

[Read: NSA program on phone records is illegal, court says]

He called for the immediate repeal of the Patriot Act and passage of his Fourth Amendment Protection and Preservation Act, which would prohibit federal, state or local governments from obtaining a person's records unless the person gives consent or there is a warrant involved.

"It is the duty of elected officials to protect the rights of all Americans," Paul said.

The decision comes as a debate on Capitol Hill over renewing the Patriot Act is laying bare fissures within the Republican Party. Lawmakers have until the end of the month to decide whether to renew expiring provisions of the bill. Senate Majority Leader Mitch McConnell (R-Ky.) said he plans to put forward a bill that would renew the Patriot Act as is, without any changes to the bulk collection programs. A bipartisan group of legislators have put forward the USA Freedom Act, which would end bulk collection of records. Cruz co-sponsored the bill.

Cruz called for the passage of the USA Freedom Act in a statement Thursday, stating that it ends the NSA's collection of data but still allows the government to get information and find terrorists "when it has sufficient justification" and can support doing so.

“The court’s ruling today confirms what the American public already knew: The National Security Agency’s data collection program went too far in collecting the phone records of Americans,” Cruz said.

Paul has said he wants to repeal the Patriot Act. But he doesn't like the USA Freedom Act either, because he believes it doesn't go far enough.

On the campaign trail, Paul can sometimes appear aloof, but he stirs when talking about the government spying on Americans, conveying his views with a passion rarely seen from him on other subjects. He rails against the government spying on its citizens, using it as the linchpin of his argument that the government should stop meddling in peoples' lives. Crowds cheer and whoop when he calls for an end to the collection or mentions the Fourth Amendment.

"May the Fourth Amendment be with you!" a man in Grand Rapids, Mich., yelled at a Paul rally May 4.

Paul and the conservative group Freedomworks sued the Obama administration and the NSA last year, claiming that the bulk collection of metadata violated the Fourth Amendment. The suit was put on hold last fall.

In Michigan on Monday, Paul gave a history lesson on the Fourth Amendment and how it was a response to British writs of assistance.

"I've got news for the government: Mr. Verizon is not a person," Paul said. "Someone’s got to wake the country up and say you can't collect everyone’s records, all of the time, all of your phone records, and think that that’s not an invasion of our privacy and a violation of the Fourth Amendment."

Paul told the crowd that he would stop the collection of information by executive order on his first day in the White House. And the crowd cheered.