(Update: 10:15 ET: Senate fails to extend expiring Patriot Act measures late Sunday. They will expire at midnight. Here is our new coverage in a separate post.)

CIA Director John Brennan said terrorists are heavily monitoring the Senate's 11th-hour vote Sunday to stop three surveillance provisions of the USA Patriot Act from expiring at midnight today.

“I think terrorist elements have watched very carefully what has happened here in the United States. Whether or not it’s disclosures of classified information, or whether it's changes in the law and policies, they’re looking for the seams to operate within," Brennan said on CBS's Face the Nation. "This is something that we can't afford to deal with right now, because if you look at the horrific terrorist attacks and violence that's being perpetrated around the globe, we need to keep our country safe."

Congress was set to begin debate Sunday at 4 pm ET. The floor session is airing live on C-SPAN here. (Floor session, without a vote, has recessed until around 6:30 pm ET. The session returned about 6:25 pm ET. Senate temporarily recessed again around 8:30 pm ET. (It appears that the three provisions at issue will expire at midnight.)

At issue is the USA Freedom Act, which addresses three expiring measures of the USA Patriot Act. The House approved the measure two weeks ago. Among the expiring provisions, they include the legal authority for the bulk telephone metadata program Edward Snowden disclosed, roving wiretaps, and the so-called "lone-wolf" measure. The House extended those provisions through 2019.

President Barack Obama said he'd sign the measure immediately after Senate passage.

"This is a matter of national security. Terrorists like al Qaeda and ISIL aren't suddenly going to stop plotting against us at midnight tomorrow. And we shouldn’t surrender the tools that help keep us safe. It would be irresponsible. It would be reckless. And we shouldn't allow it to happen," the president said during his weekly address Saturday.

If approved, the bulk telephone metadata would be taken from the hands of the National Security Agency, and it would reside with the nation's telcos. The data still could be searched with a warrant from the Secret Foreign Intelligence Surveillance Court (FISA Court) if the authorities maintain it's relevant to a terror to a terror investigation. The normal constitutional Fourth Amendment probable cause standard does not apply.

The metadata includes phone numbers of each party to a call, calling card numbers, the length and time of the calls, and the international mobile subscriber identity number of calls made on mobile phones.

What's the "roving wiretap" provision? It allows US authorities to obtain a warrant from the FISA Court without having to identify the target. What's more, the nation's spies may tap a suspect's line from one number to the next as they change devices.

The "lone wolf" provision, meanwhile, allows FISA Court warrants to electronically monitor somebody. The authorities do not need to show that the suspect is an agent of a foreign power or even linked to terrorism.

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