Supporters of a compromise bill on bulk surveillance by the National Security Agency said that there are enough votes in the Senate to pass the legislation and that efforts to block its passage at Sunday’s Senate session would pose a threat to national security.

“At this point, I think the question is not really about whether we’ll get this passed but when,” Sen. Mike Lee (R-Utah), sponsor of the USA Freedom Act, said Sunday on CNN’s "State of the Union." "This is a good day for the American people, whose rights will be protected, whose Fourth Amendment and privacy interests will be defended. At the same time, their national security interests will also be protected and preserved."

The Senate will reconvene Sunday, hours before the Patriot Act expires at midnight, after it rejected the compromise bill just over a week ago. The House-passed USA Freedom Act would keep key provisions of the Patriot Act but prohibit the controversial mass collection of phone records by the government. Private telephone companies would hold the records for 18 months instead.

Sen. Rand Paul (R-Ky.), one of the main opponents of the Patriot Act who has promised to repeal it if elected president, has vowed to block the passage of the USA Freedom Act or the extension of the current law. "Let me be clear: I acknowledge the need for a robust intelligence agency and for a vigilant national security. Sometimes when the problem is big enough, you just have to start over," Paul said in a statement to Politico.

Lee said that while he shares Paul's privacy concerns over the mass collection of bulk phone records, he does not agree with Paul's strategy. He said the USA Freedom Act would solve the underlying problem, as the bill would require phone companies -- not the government -- to store the call records.

If Paul successfully uses a procedural method to delay the vote Sunday and the Patriot Act expires, the earliest the Senate could pass the bill is Tuesday.

Sen. Angus King (I-Maine), a member of the Senate Intelligence Committee, said that if the vote is blocked Sunday, he is concerned about the potential implications on national security during the window of time after the law expires and before the Senate takes up the bill again.

"I would hope that those who are making a big deal of standing in the way and objecting and blocking realize all they're doing is slowing something down that will happen in two or three days . . . and there is a risk created for those periods," King said on CNN.

President Obama and Attorney General Loretta Lynch have called for the passage of the USA Freedom Act. The administration has warned that the FBI will lose legal tools that allow the government to conduct national security investigations during a time of heightened terrorism threats.

The impact of the Patriot Act expiring may not be apparent right away, said Gen. Michael Hayden, former NSA and CIA director. But the gap could pose a long-term problem, as intelligence gathering is done "piece by piece, thread by thread," he said.

"You're giving up threads. It may not make a difference for a while. But then again, it might. And over the longer term, I'm willing to wager . . . that it will, indeed, make a difference," Hayden said on "Fox News Sunday."