WASHINGTON — Call it a Sunday Senate showdown: a rare weekend Capitol Hill battle over the Patriot Act, which will expire at midnight Sunday unless Congress acts. The high-stakes face-off between national security and privacy rights could end up in a stalemate unless someone can convince members of the upper chamber to compromise.

Could this be a job for U.S. Sen. Elizabeth Warren — the congressional rabble-rouser from the Bay State?

On one far end of the three-way conflict is Senate Majority Leader Mitch McConnell, who wants a wholesale renewal of the law. On the other side of the spectrum is Sen. Rand Paul, the GOP presidential candidate from Kentucky, who wants to kill the law altogether.

In the middle are Democrats, including President Obama, pressuring McConnell to back a bipartisan bill that would rein in the National Security Agency’s phone data collection program, which a federal judge recently struck down. That measure, the USA Freedom Act, passed with broad bipartisan support in the House last week and would allow the government to still obtain cellphone data collection, but only with warrants.

Unlike other down-to-the wire Senate battles, which usually result in some eleventh hour solution, both Paul and McConnell have dug in their heels.

So who better than Warren, who has shown a penchant for vocally drumming up support for and against high-profile legislation, not only to get her desired legislative outcome but also to impact the presidential campaign debate, to lead the charge?

But it doesn’t seem that Warren is ready to rally.

Warren said she’d be there Sunday, explaining yesterday that “a court has now ruled that the Patriot Act is not lawful.”

Actually, a federal court ruled the NSA phone program was not authorized by the language of the act; it didn’t rule on the legality of the law itself.

Warren continued, “We were in the wrong place with the Patriot Act.” So she’s backing the House-passed measure. But not wholeheartedly: “USA Freedom is a step in the right direction in terms of providing protections for data security and to make sure that the government does not overreach in its wholesale collection of data. But I think it’s only a first step. And that there’s more work to be done.”

While national security has never been one of Warren’s championed causes, the issue of protecting citizens’ privacy and 4th Amendment rights gels nicely with her progressive platform. But it seems that on Sunday, the debate will happen without a Warren wing revolt.

Matt Stout contributed to this report.