"The nuclear option is a parliamentary procedure that allows the United States Senate to override a rule – specifically the 60-vote rule to close debate – by a simple majority of 51 votes, rather than the two-thirds supermajority normally required to amend the rules. The option is invoked when the majority leader raises a point of order that only a simple majority is needed to close debate on certain matters. The presiding officer denies the point of order based on Senate rules, but the ruling of the chair is then appealed and overturned by majority vote, establishing new precedent.
This procedure effectively allows the Senate to decide any issue by simple majority vote, regardless of existing procedural rules such as Rule XXII which requires the consent of 60 senators (out of 100) to end a filibuster for legislation, and 67 for amending a Senate rule. The term "nuclear option" is an analogy to nuclear weapons being the most extreme option in warfare." wiki
"The "nuclear option" is invoked when a simple majority of the Senate overrides the normal consequences of the rules above. Following a failed cloture vote, the majority leader raises a point of order that Rule XXII should be interpreted – or disregarded on constitutional grounds – to require only a simple majority to invoke cloture on a certain type of business, such as nominations. The presiding officer, relying on the advice of the Senate Parliamentarian, then denies the point of order based upon rules and precedent. But the ruling of the chair is then appealed, and is overturned by simple majority vote" wiki
The rule requiring 2/3 of the Senate voting in the affirmative for closure of debate (cloture) on legislation is not part of the Constitution. It is simply an internally decided rule of the Senate. The rule has been different in the past and can be changed whenever the Senate votes to do so.
The Republican Party holds control of both houses of Congress until the end of 2018. In the new Congress the Democrats will control the House of Representatives and the GOP will control the Senate with a majority of 53.
It is clear to me that the Democratic House will not cooperate with President Trump's legislative agenda on anything except possibly infrastructure improvements (roads, bridges, etc.).
Legislation, unlike presidential appointments to the courts, ambassadorships, etc., requires the action of both houses. That being the case it is to be expected that no further legislation regarding Trumps MAGA agenda will be passed in the final two years of Trump's first term.
Therefore I see no reason why Senator McConnell should not attempt to change the 2/3 Cloture Rule so that there is a chance to pass the Second Phase Tax bill and the Border Security funding bill in the Lame Duck. To change the rule would require a simple majority in the Senate. The GOP has 51 seats in the Senate. There are several "shaky" Republican senators who may not be reliable in such an attempt. Senator Flake of Arizona has shown himself to no longer be under Republican caucus control and would likely vote against a rule change. I think he is probably going to re-enter politics as a Democrat after he leaves the Senate in January.
Without Flake it would be difficult but not impossible to get a 50-50 split on a vote to change the rule. In that case Vice President Pence could break the tie as presiding officer of the Senate.
I think this is worth a try.
The argument that the Democrats would use this new rule when they eventually regain control of the Senate is laughable. The Republican principle here should be "lets do it to them before they do it to us." pl