One of the long-shot entrants in the "causes of imminent government collapse" suddenly burst back into the lead Thursday, as Senate Republicans blocked two key Obama appointees. Remember the "nuclear option" threat to revise Senate procedural rules? It's poised to return, just in time to rip open the still-healing wounds from the shutdown.

As you're probably aware, Senate rules allow senators to filibuster certain legislation and votes. If a senator chooses to do so, a super-majority of the body must vote to end the filibuster, a vote called cloture. In recent years, those filibusters have become less formal — rarely including the classic talk-until-you-drop-from-exhaustion component — and much more common. (See James Fallows at The Atlantic.) It's become so common that freshman Sen. Ted Cruz of Texas called the supermajority needed to end a filibuster the "traditional 60-vote threshhold."

Over the course of the spring, Senate Democrats repeatedly threatened to revoke the right to filibuster presidential nominees. The rules change itself — melodramatically dubbed the "nuclear option" — only requires a majority of senators to vote in support, a margin that Senate Majority Leader Harry Reid claimed to be able to meet. (We weren't so sure.) The Democrats backed off that threat in July, giving up two Obama nominees to assure that none of the a large group of others would face a filibuster. Peace reigned, for a while.

Earlier this week, Sen. Patrick Leahy of Vermont revived the idea of the rules change. The Huffington Post reports:

The pressure to change Senate rules and strip Republicans of their power to filibuster certain judicial nominees "would be almost insurmountable" if Republicans block [Patricia] Millet's confirmation vote to the D.C. Circuit Court of Appeals, Leahy said at an event advocating Millett.

Reid agreed. And on Thursday, Millett was blocked. She received a majority of the Senate's support, but not enough to reach cloture. At the same time, Senate Republicans blocked the president's nominee to lead Fannie Mae and Freddie Mac, Rep. Mel Watt of North Carolina. Watt, too, received a majority of the Senate's support, but failed to reach cloture. Sen. Claire McCaskill of Missouri suggested the votes were just another form of shutdown:

"There are two ways to shut down the gov: one, by denying funding; two, by blocking appointees for false political reasons."

In Millett's case, the "false political reasons" are mostly that her appointment would shift the balance on the D.C. Circuit in the Democrats' favor. In Watt's case, Republicans raised questions about his qualifications.

There's one more reason the nuclear option may have gotten more likely. In our assessment of support for the rules earlier this year, we found that Reid was flirting with the 50-vote mark—in part because the death of New Jersey senator Frank Lautenberg meant that Republican Jeff Chiesa joined the body. On Thursday, that changed, with the swearing-in of former Newark Mayor Cory Booker. That additional vote might make the nuclear option more appealing to Democratic leaders.

Everyone was watching the clock, waiting for the Congressional budget committee's December 13 deadline to arrive before assuming the Congress would reach a point of crisis. But Congress is far too good at provoking crisis to wait that long.