It is those higher vote requirements that are the intended target of the nuclear option. Under that option, the Republicans would use a majority vote (rather than 67 votes) to change the filibuster rule from 60 votes to 51 votes.
That would implicate Senate Rule V, which says that the Senate's rules shall continue from one Senate to the next "unless they are changed as provided in these rules."
Republicans say the combination of Rule V and open-ended Democratic filibusters of judges can result in unconstitutional entrenchment, rendering Rule V invalid. This is why some Republicans are calling it the "constitutional option." Democrats say the rules are clear and fair, and should not be unilaterally changed in the middle of a heated dispute.
Overall, Republicans and their supporters say there is a constitutional duty to provide the Senate's advice and/or consent through an up-or-down majority vote on each presidential nominee. To use a filibuster to block a majority vote is to rewrite the Constitution and undermine the fundamental concept of majority rule, they say.
Democrats and their supporters stress that the Senate must follow its own rules when carrying out advice and consent responsibilities. The filibuster rules are designed to protect the interests of the minority party by creating an incentive for majority senators to reach out for compromise rather than adopting a winner-take-all approach. The result of compromise is almost always better government, they say.
"Democratic senators represent a majority of the population, but they are a minority in the Senate," says Erwin Chemerinsky, a constitutional law professor at Duke University in Durham, N.C. "The filibuster in part is a reflection of that - the way in which senators who represent the majority can act as a check on the majority of senators who represent a minority of the population."
Professor Chemerinsky says the Republican focus on a majority vote is misplaced. "The filibuster doesn't change the fact that to be confirmed it takes a majority," he says. "The filibuster's role is what number of votes does it take to end debate. And there is nothing in the Constitution about the number of votes it takes to end debate."