Congress' debate over domestic surveillance is scrambling partisan divisions in the Senate as libertarian-minded Republicans defy their leaders to make common cause with liberal Democrats.

Tea party conservative Sen. Mike Lee of Utah is pairing with liberal stalwart Sen. Patrick Leahy of Vermont to push for Senate passage of the USA Freedom Act, which would end the National Security Agency's collection and storage of domestic calling records after a six-month transition period. Already approved by the House on a large bipartisan vote, the bill could come to a vote in the Senate on Friday, but is opposed by GOP leaders who prefer to extend the existing call collection program unaltered.

Other Republican backers of the legislation include GOP Sens. Ted Cruz of Texas, Dean Heller of Nevada, Lisa Murkowski of Alaska and Steve Daines of Montana, joining most Democrats. Sen. Rand Paul, R-Ky., like Cruz a candidate for president, takes it even further and wants the program to expire entirely, rather than be overhauled.

"Bipartisanship can be about two people believing in the same thing but just being in different parties," Paul said as he held the Senate floor for nearly 11 hours earlier this week to protest the NSA bulk collection program. "You can have true, healthy bipartisanship, Republican, Democrat, independent coming together on a constitutional principle."

Paul was joined during his long stand on the Senate floor by a parade of lawmakers of both parties, but primarily Democrats, who each took a turn speaking to give the Kentuckian a break.

"We're not usually on the same page about a lot of things, but our constituents on the right and left feel very passionately that if they're not doing anything wrong that the government shouldn't be in their business," Democratic Sen. Martin Heinrich of New Mexico said after backing Paul up on the floor. "It's not a left-right thing — it's as true in Taos, N.M., as it is in Kentucky."

The GOP libertarian streak, favoring individual liberties and opposing government intervention, seems particularly pronounced in newer GOP arrivals to the Senate from Western states. It's also a feature of some of the tea party-backed Republicans in both the Senate and the House. Taken to extremes it can amount to an isolationist worldview and Paul has softened some stances as he campaigns for president.

"Montana has a very populist streak, wary of big government," Daines said in explaining his stance. "It's not necessarily a Republican or Democrat issue ... it crosses the partisan divide."

The USA Freedom Act would preserve the NSA's ability to query phone company records in search of terror connections, while maintaining other surveillance powers set to expire. But it looks short of votes to pass, as does a two-month extension of existing law supported by Senate GOP leaders. That's left Senate leaders weighing a potentially even shorter extension. Without congressional action, bulk collection and all the other programs within the Patriot Act expire at the end of this month.

For some of the Republicans allying themselves with Democrats on the USA Freedom Act, it's not an entirely comfortable place to be. Lee sent out a mass email to supporters on Thursday asking them to sign a petition opposing the NSA, claiming that "liberals" were seeking to continue government spying — even though it's his own party's leaders who want to keep the current program running unchecked.

And Cruz responded to a reporter's question about the unusual coalition on the issue by remarking: "I certainly hope we see a whole lot more Republicans" joining those like him who back the USA Freedom Act.

Yet similar left-right coalitions could resurface on other issues, including medical marijuana and criminal sentencing reform. Paul and Leahy are already working together on a bill, opposed by key Republicans, to limit the use of mandatory minimum sentences.

"It's just a reality we have to deal with. We've got people in different places," said Sen. John Thune, R-S.D., a member of GOP leadership. "This is not going to be the only issue where that's true."