In recent years, final Senate action on several presidential nominations for federal judgeships has been impeded by filibusters or threatened filibusters. In response, some leading Senators have called for the Senate to change its procedures to prevent filibusters, or make them harder to sustain, at least on this class of business. Filibusters are possible largely because for most matters, including nominations, existing Senate procedures establish neither limits on the time available for consideration nor means by which a voting majority may impose such limits. In this sense, existing Senate rules largely lack provision for effective majoritarian consideration limits. Accordingly, advocates of change in this area have focused on procedural changes that would afford more effective means for a majority to limit consideration. Existing Senate rules and procedures, however, also place potentially substantial obstacles in the way of adopting changes in these rules and procedures. In particular, the lack of effective majoritarian consideration limits also applies to the procedures under which the Senate normally considers proposals for procedural change. As a result, advocates of more effective consideration limits have sought alternative means of instituting procedural changes that would not be subject to these difficulties. Beginning in the 108 th Congress (2003-2004), the term "nuclear option" has often been used to refer to a procedural course of action that would meet this requirement of bypassing the obstacles posed by the usual procedures for considering procedural changes. Critics of this form of action, however, have used this term also to connote that unilateral resort to such a course by a majority might undermine "traditional" practices of comity within the Senate, especially the expectations of predictability through consensual arrangements that have hitherto been held to characterize the body. Because of this connotation, some advocates of this form of action have come to prefer the term "constitutional option." This designation appears to connote that most of the courses of action currently under consideration would rely on an appeal to constitutional requirements as grounds for instituting consideration limits. This report reserves the term "constitutional option" for those courses of action that depend specifically on constitutional points of order, as explained in the section on " The "Constitutional Option" ." The term "nuclear option" is here used only to indicate that such a course of action would constitute an alternative to "conventional" proceedings because of its capacity to cut comprehensively through the normal difficulties of achieving procedural change. In this usage, any form of "nuclear option" would afford the Senate means to circumvent the obstacles to change posed by the usual forms of proceeding. This usage leaves open whether a course of action could achieve its result without compelling the Senate to set aside requirements of its existing procedures in the process. A course that did require action at variance with established principles underlying the system of Senate procedure might be considered "nuclear" in a more fundamental sense. The reason, as explained in the section on " Overcoming Entrenchment ," is that it would presumably constitute precedent for subsequent departures of the same kind. It is one purpose of the following discussion to identify the extent to which various courses of action described would or would not be "nuclear" in this strong sense. The chief intent of this examination is to identify some specific courses of procedural action that might be used to carry out a "nuclear option" in the broad sense just defined. It focuses on clarifying the specific features of each course that might enable the Senate to avoid the obstacles to change posed by more conventional ways of proceeding. It indicates what provisions of existing procedures might pose difficulties for implementing various courses of action, as well as possible procedural responses by which proponents of such action might address these difficulties. The discussion also identifies the features that specifically distinguish some of these courses of action as "constitutional options." In addition, however, it identifies points at which the courses of action might require proceedings at variance with existing requirements. On the basis of this examination, it is possible in conclusion to identify some implications that resort to a "nuclear option" might have for the subsequent condition of Senate procedure. Showing how a course of procedural action represents a "nuclear option" involves identifying the ways in which it may bypass or overcome the obstacles posed by the usual procedures. To enable this examination, the discussion begins by describing the nature of these obstacles and indicating how they are grounded in the existing structure of Senate procedure. These observations make it possible to explain more specifically not only what a "nuclear option" must accomplish, but also why resort to proceedings of this kind may appear attractive or necessary in the first place. The question of enhancing the ability of the Senate to limit consideration of matters has dominated the procedural history of the body for well over a century. Part of the reason for this persistence is that Senate procedures have always lacked effective limits on consideration. This lack of consideration limits may often enable opponents of a proposal to block its approval, even if it is supported by a majority, by extending its consideration indefinitely, thereby preventing the Senate from ever being able to reach a vote on it. It is delaying actions of this kind that are colloquially, but universally, known as filibustering. This lack of effective consideration limits also applies to the procedures normally used for consideration of proposals for procedural change. In particular, it extends to the consideration of any proposal to institute additional consideration limits. Proposals to constrain filibustering can be filibustered. In this way, the existing lack of consideration limits operates as a continuing obstacle to the establishment of new consideration limits. The persistence in the Senate of the question of limiting consideration, however, also arises from a second cause. Certain elements of the Senate's procedural system have the effect of requiring that its established procedures remain continuously in effect. As a result, a proposal to institute more effective means of limiting consideration would have to be considered in accordance with the already existing procedures. The principle that existing Senate procedures remain always in effect then combines with the lack of consideration limits under existing procedures to make it hard for the Senate to adopt more effective consideration limits. It is in this sense that Senate rules have been described as "entrenched" against their own change. This section considers more specifically these two features of Senate procedure, which together bring about its entrenchment. It examines first the procedural provisions that result in the general lack of consideration limits, then the principles that result in the continuous force of the existing system of procedure. On the basis of this discussion it will be possible to consider what characteristics a "nuclear option" would have to possess in order to succeed in overcoming the entrenchment of Senate procedure so as to permit the adoption of additional limits on consideration. Senate procedure is governed not only by the Standing Rules of the chamber, but also by standing and special orders, pertinent provisions of the Constitution and of statute, the body of precedent formed by past rulings on procedural questions, and informally accepted practices. For most matters, none of these procedural standards either places any restrictions on how long consideration may last, or explicitly establishes any means for a simple majority of Senators voting to impose such restrictions. In general, only by a super-majority may the Senate apply the limits on consideration specified in Senate Rule XXII, an action known as invoking cloture. Otherwise, the Senate may in general place agreed restrictions on consideration of a question only by unanimous consent. Some accounts suggest that the most likely purpose of resort to a "nuclear option" under current conditions would be to permit the Senate to limit consideration of a nomination by a simple majority vote, rather than a super-majority. In fact, however, Senate procedures already require only a simple majority for the approval of almost any substantive proposal, including a nomination. (The requisite number has often lately been referred to as "51 votes" although, in fact, it is smaller when not all Senators vote.) The effect of Senate procedures, in general, is to require a super-majority not for the approval of items of business, but only for the imposition of limits on their consideration, so as to ensure that votes on their approval can occur. Under these arrangements, even if a proposal is supported by a majority, opponents may be able, by filibuster, to prevent the Senate from reaching a vote on it, unless supporters are numerous enough to invoke cloture. It is from desire to avoid possible filibusters that Senate practice has historically fostered the settlement of issues through collegial processes of seeking consensual agreement. Inasmuch as filibusters are defined by the intent of the participants to block action, their conduct is not limited to the use of any specified form of procedure. Although filibusters are commonly thought of as carried out through extended debate, they may also be conducted by a wide variety of other procedural means. Correspondingly, although cloture is widely understood as a motion for bringing debate to a close, it also restricts certain other actions that could be used for purposes of delay. Senate procedure also permits debate on many procedural motions. In particular, a motion that the Senate proceed to consider a bill or resolution is debatable under most circumstances (by contrast, however, present practice permits the Senate to proceed to consider a nomination on a non-debatable motion). For this reason, if opponents of a matter persist in a filibuster, reaching a final vote may require supporters to secure super-majority support for cloture or other limits on consideration multiple times, on each of several essential questions that may arise in the course of consideration. For a few specific questions, nevertheless, Senate rules or other procedures do establish limits on consideration, and, as discussed in the next section, some of these might play a role in the implementation of a "nuclear option," All these conditions of consideration apply to the conduct of Senate business generally; they are not specific to the consideration of proposals for procedural change. Only because the Senate's general rules of procedure also apply specifically to the consideration of proposed changes in procedure do they contribute to the entrenchment of the existing procedures. Specifically, the lack of effective majoritarian consideration limits in existing procedure tends to entrench itself by constituting the chief obstacle to its own change.