Sen. Rand Paul, R-Ky., with the aid of Sens. Martin Heinrich, Mike Lee and Ron Wyden (and maybe others by midnight), may have stopped Senate Majority Leader Mitch McConnell’s PATRIOT Act extension bills (if the filibuster lasts until midnight) from consideration before Memorial Day.

There’s a ton of confusion about what’s happening right now in the Senate regarding surveillance reform. Not just about the general brinksmanship that’s been developing, but about why, right now, Paul is filibustering, along with Heinrich, Lee, Wyden and perhaps others’ help (which is critical for long filibusters). Both Paul and Wyden have said that they would filibuster reauthorization of the PATRIOT Act, but that was supposed to happen Thursday – reauthorization isn’t even up for debate right now.

One suggestion is that the filibuster now is useless – that nothing was scheduled today, so Paul could filibuster without actually stopping the USA FREEDOM Act and without allowing Section 215 to sunset.

It’s not. Or, at least, it may not be. In fact, it could be a very clever reversal of the environment McConnell has created, which was clearly designed to put senators in the middle on surveillance in a vice: Either the USA FREEDOM Act passes or fails (McConnell has said he expects it to fail), or, on the other hand, senators will have to vote on a 2-month reauthorization or nothing. If USA FREEDOM — which offers some reforms but also some sacrifices (Sunlight has been opposed since last year because of said sacrifices) — fails, will 41 senators allow Section 215 to sunset instead of supporting a short-term reauthorization?

We don’t know. McConnell has also said he expects senators to be swayed by USA FREEDOM’s possible failure.

Those are high stakes for reformers.

The critical factors that inform the rest of this: The House has passed a version of the USA FREEDOM Act; it has not passed any kind of “clean” reauthorization (one that doesn’t include any changes); the last time the House is in session before sunset occurs is Thursday at 3:00 p.m.; and the House has indicated they are not willing to acquiesce to the results of the Senate’s brinksmanship. This is where the brilliance lies: Senate procedure.

What does the currently ongoing filibuster have to do with this? It’s not just that it stalls the vote in the Senate and wedges it up closer to Section 215’s expiration. If Paul and his allies get to midnight tonight, as far as we can tell, it stops the Senate from considering any bill other than the House-passed USA FREEDOM Act, or, by default, sunset before Saturday. Without this filibuster, McConnell could have moved today to proceed on from the trade vote to USA FREEDOM or the 2-month reauthorization (though the Senate will have a cloture vote on trade tomorrow no matter what), and in turn begun the cloture process, which would have matured Friday. While the House is supposed to be out on Friday, keeping the House for another day, versus through the weekend and into Memorial Day, is a bit different.

Here’s a lengthy write-up by the Congressional Research Service about filibuster rules in the Senate. Here’s a more easily synthesizable walkthrough. Below is a summary of how they apply to what’s going on. (Huge thanks to Senate Parliamentarian Elizabeth MacDonough for helping me through this.)

When the Senate invokes cloture, it limits the debate to 30 additional hours (which means no vote can come up). But why is the filibuster happening now, during the trade debate? Because not only does one need to invoke cloture, get 60 votes to stop a senator from talking and then wait (up to) 30 hours to move on from debate, someone needs to file a motion for cloture, and, after filing for cloture, it’s only on the second day that that cloture has matured.

In other words: File for cloture, then on the second day move to invoke cloture if there are 60 votes (thereby limiting debate to an additional 30 hours), and only then can the Senate move.

So, if McConnell had filed for cloture on Monday, the first day the reauthorization bills or USA FREEDOM could have arrived would have been Wednesday, and, with a filibuster, the first vote 30 hours later. On Tuesday, it would have been Thursday.

We, and others, expected him to do so on Tuesday.

But, surprisingly, McConnell did not file for cloture yesterday. Indeed, we just called the Senate Parliamentarian, and have confirmed that the Senate version of USA FREEDOM was still in committee, and both the House version of USAF and the two-month reauthorization were still “on the calendar” (meaning it hasn’t been brought to the floor, and therefore, there hasn’t been any filing for cloture, because one can only do so on the current measure being considered – which, right now, is trade).

If McConnell thought the House would stay till Friday to pass whatever the Senate passed, assuming this filibuster goes to midnight and cloture is still required on whatever bill comes up, it appears the Senate cannot act until Saturday, and, in addition to that, and would still have to wait until 30 hours after cloture is invoked (which again, would be Saturday and require 60 votes). After those 30 hours, maybe a bill goes back to the House.

So, although this filibuster is going on during the trade debate, it is profoundly impactful on whether we end up with USA FREEDOM Act, full sunset or whether there will even be time to consider a “clean” reauthorization.

Assuming the House does not stay in session, as it has strongly suggested it will not, these senators appear to have moved us further into a world where there are only two outcomes on surveillance reform: House-passed USA FREEDOM Act, or sunset.