Enough Republicans have said they oppose it to make it unlikely to be used to avoid a government shutdown. But what does that mean and why is it, well, nuclear?
WHAT IS THE NUCLEAR OPTION?
Under normal rules, the Senate requires a simple majority to pass bills, but any Senator can block one with what is known as a filibuster, or ongoing debate. To move past a filibuster, the Senate needs 60 of 100 votes. With the chamber split 51-49 Republicans to Democrats, getting to 60 votes can be a high hurdle.
The majority party can change the rules and allow an up-or-down vote, but doing so is called "the nuclear option" because it goes against Senate traditions of bipartisanship and debate. And, importantly, it can have unintended consequences.
IT HAS HAPPENED BEFORE
This procedural maneuver has recent precedent. In 2017, Republicans used the "nuclear option" to force through the appointment of Neil Gorsuch to the Supreme Court. Supreme Court nominees had been exempted under new rules the Democrats set for judicial appointments in 2013.
At that time, Democrats were in the majority under the leadership of Sen. Harry Reid of Nevada and upset about the blockage of President Barack Obama's nominees to a powerful appellate court.
At the time, now-Senate Majority Leader Mitch McConnell warned Democrats the strategy would backfire: "I say to my friends on the other side of the aisle, you will regret this, and you may regret it a lot sooner than you think."
Before 1975, it was even tougher for presidents to get their nominations through because two-thirds of the senators present and voting had to agree to move forward.
WHY IT IS EXPLOSIVE
Such a rule change would be a momentous shift for the Senate, which traditionally operates via bipartisanship and consent from all senators. Some believe it could begin to unravel Senate traditions at a hyper-partisan moment in politics and perhaps end up in the complete elimination of the filibuster even for legislation--which would mean an entirely different Senate from the one that's existed for decades.
Senate experts note that the filibuster is not enshrined in the Constitution, but McConnell is an institutionalist who has made clear he did not favor invoking the nuclear option and did so grudgingly on Gorsuch's nomination.