The Senate will gavel in a rare weekend session Sunday afternoon, just hours ahead of the midnight expiration of controversial Patriot Act provisions, but the path to a solution remains very much unclear.

At issue is Section 215 of the 2001 Patriot Act, which is used as legal justification for the National Security Agency’s bulk telephone data collection, the program revealed two years ago by leaker Edward Snowden. For the most part, lawmakers currently fall into three camps: those who would like to see the law reauthorized and the program continue unchanged; those who support a reform measure that would end the bulk data collection; and those who would prefer to see the entire Patriot Act expire.

The Sunday session is a direct result of the Senate’s failure to find a solution during a Friday night session last week that carried into the early hours of Saturday, with lawmakers equally eager to solve the problem and make it home for the Memorial Day recess. Two attempts to clear the 60-vote threshold failed: one involved reform legislation that passed overwhelmingly in the House, and the other was to extend the program for two months, thus allowing time for the debate to continue.

After those two votes failed, Majority Leader Mitch McConnell tried to extend the program for one week, then four days, then two days and finally a single day, but opponents objected each time, after which McConnell announced the session this Sunday.

“One more opportunity to act responsibly to not allow this program to expire,” McConnell said. “This is a high-threat period and we know what’s going on overseas, we know what’s been tried here at home. My colleagues, do we really want this law to expire? We’ve got a week to discuss it; we’ll have one day to do it. So we better be ready next Sunday afternoon to prevent the country from being endangered by the total expiration of the program.”

It remains unclear, however, what direction the session will take. McConnell entered motions to recommit for both the House-passed USA Freedom Act and the short-term, two-month extension, which means he can bring both of those up for a vote again. He has not indicated, however, whether either will get another vote Sunday.

Proponents of the USA Freedom Act – which passed the House before recess by a 338-88 margin – argue that it is the only way forward, particularly just hours before the deadline. The House isn’t scheduled to return until Monday afternoon, after the program expires, thus making any short-term fix extremely unlikely. Though the Senate failed to move the House bill by a 57-42 margin last week, there is some confidence that three or more votes could be picked up with the deadline imminent.

Utah Republican Sen. Mike Lee, one of the co-sponsors and most vocal supporters of the USA Freedom Act, said he thinks there is a “good chance” it would pass if brought back up for a vote Sunday. Lee said he’s been “working the phones aggressively” during the recess with colleagues who are on the fence.

“There were several people who voted against it Friday night who I know felt that they’d rather have something pass rather than nothing,” he told RealClearPolitics in an interview. “I really think they would have voted for it and I’m even more confident that we’ll have several who voted against it who would vote for it now.”

Part of the problem for McConnell, who preferred a clean reauthorization of the Patriot Act provisions without any changes, as well as supporters of the USA Freedom Act, is Kentucky Sen. Rand Paul, a 2016 presidential candidate and extremely vocal critic of the NSA’s domestic surveillance practices. Paul staged a filibuster last week, delaying consideration of the Patriot Act provisions, and later blocked multiple attempts by McConnell to renew the program for even as little as one day. He does not support the House bill and voted against it last Friday.

Paul has been forcefully fundraising off his recent Senate action, sending out a slew of emails to supporters during the recess talking about his stance against the NSA and asking for donations. In a lengthy email Friday morning, the libertarian-leaning senator said his 10-½ hour filibuster “has thrown Washington, D.C. into turmoil.”

“When the Senate comes back into session on May 31st, there will be just eight hours for spy state apologists to reach a deal to keep these programs going,” Paul wrote in the email. “Eight hours! I'm determined to do whatever I can to stop them – regardless of the ugly smears I face by both the press and surveillance state backers.”

A super PAC supporting Paul also released a Wrestlemania-style video Friday in anticipation of the special session. It featured Paul’s face Photoshopped onto a buff wrestler’s body and alluded to a showdown between him and President Obama – with the Kentucky senator labeled “The Rand Man” and an announcer calling him a “defender of freedom.” The ad highlighted how important the NSA fight is for Paul’s White House aspirations.

McConnell, who supports his fellow home state senator’s presidential run, has said that he and Paul simply have a difference of opinion on the issue, and that it’s not personal, according to the Associated Press. The majority leader also said that the wide margin of support in the House for the USA Freedom Act “makes it pretty challenging to extend the law as it is."

Lee said the choice is simply to pass the House-passed bill or let the surveillance authorities expire, and that he believes there is no alternative path forward because of the serious time constraints.

The pressure on McConnell to halt his opposition to the House bill has come from all sides. Obama supports the House measure and the White House has increasingly called this week for the Senate to pass it. Democrats have also applied pressure after nearly unanimously supporting the legislation last week – with independent Sen. Angus King, who caucuses with the Democrats, the only one voting against cloture. Democratic leadership – Minority Leader Harry Reid and Sens. Dick Durbin, Chuck Schumer and Patty Murray – released a joint statement Thursday pushing McConnell to pass the House bill.

“It's been five days since we adjourned while punting this issue until the 11th hour,” the senators said. “In that time, we have not moved any closer towards a solution but we have moved closer to the expiration of these authorities that you insist must not occur. It is time to abandon your opposition to the USA Freedom Act, and pass this bill.”

Lee said he could have potentially supported a short-term extension last week with the goal being to debate amendments to the USA Freedom Act on the Senate floor, but the window for that option has passed.

“I’ve been telling my colleagues, Republicans and Democrats, if you want the provisions at issue to expire Sunday night, do nothing,” Lee said. “If you want them not to expire, I think we’ve got exactly one option to do that, which is passing exactly what the House passed by an overwhelming margin.”

Sunday sessions in the Senate are extremely rare, with the last one coming Dec. 15, 2013 and lasting just 20 minutes, with no votes. The last time the Senate voted on a Sunday was during the fiscal cliff showdown in late December 2012. There have been only eight Sunday sessions for the Senate during Obama’s presidency.