Although party divisions sprang up almost from the First Congress, the formally structured party leadership organizations now taken for granted are a relatively modern development. Constitutionally specified leaders, namely the Speaker of the House and the President pro tempore of the Senate, can be identified since the first Congress. Other leadership posts, however, were not officially recognized until about the middle of the 19 th century, and some are 20 th century creations. The following tables identify 15 different party leadership posts beginning with the year when each is generally regarded to have been formally established. The tables herein present data on service dates, party affiliation, and other information for the following House and Senate party leadership posts: House Positions 1. Speakers of the House of Representatives, 1789-2017 2. House Republican Floor Leaders, 1899-2017 3. House Democratic Floor Leaders, 1899-2017 4. House Democratic Whips, 1901-2017 5. House Republican Whips, 1897-2017 6. House Republican Conference Chairs, 1863-2017 7. House Democratic Caucus Chairs, 1849-2017 Senate Positions 8. Presidents Pro Tempore of the Senate, 1789-2017 9. Deputy Presidents Pro Tempore of the Senate, 1977-2017 10. Permanent Acting President Pro Tempore of the Senate, 1964-2017 11. Senate Republican Floor Leaders, 1919-2017 12. Senate Democratic Floor Leaders and Conference Chairs, 1893-2017 13. Senate Republican Conference Chairs, 1893-2017 14. Senate Democratic Whips, 1913-2017 15. Senate Republican Whips, 1915-2017 This information reflects the leadership elections and appointments at the start of the 115 th Congress. Included for each post are leaders' names, party and state affiliations, and dates and Congresses of service. For most Congresses, the report indicates years of service only, except in the tables for the House Speaker and the Senate President pro tempore, both of which include specific dates of service. When a Member died while holding a leadership office, however, the date of death is included as the end-of-service date (except in Table 13 ). In cases where a leadership change occurs during the course of a Congress, exact dates of service are indicated where possible. With respect to length of service, the report includes all instances in which a Member held a particular leadership post, regardless of whether the Member held the post for the entire Congress or only a portion of it. Official congressional documents ( House Journal and Senate Journal , Congressional Record , and predecessor publications) can be used to document the tenure of the constitutionally specified leaders (i.e., Speaker and President pro tempore). The actions of the party organizations in choosing other leaders, such as floor leaders or caucus or conference chairs, frequently went unacknowledged in these sources, however. In the frequent absence of party caucus records in the latter half of the 19 th century, scholars have had to rely on secondary sources, such as memoirs and correspondence, for evidence of party leadership position-holding. The concluding portion of this report, " Source Notes and Bibliography ," provides more information about sources and the reliability of leadership lists. The changing nature of congressional leadership provides additional challenges to identifying leaders not constitutionally specified (e.g., floor leader). Even for party elected posts, determining who held other positions can be problematic in earlier Congresses. For example, identifying each party's conference (or caucus) chair often requires reliance on incomplete historical records of conference meetings or inferences made from informal practices (e.g., noting which Member nominated his party's candidate for Speaker, a motion that often fell to the conference chair). In the House, for example, it was the common practice of President Thomas Jefferson and his immediate successors to designate a Member as their principal legislative spokesman. Often these spokesmen held no other formal leadership position in the House, and Presidents frequently designated new spokesmen, or even specialized spokesmen for individual measures, as their terms progressed. As these and other "leaders" were not chosen by a congressional party group or by a party leader such as the Speaker, these presidential designees have not been included here as "party leaders." Most historians who study the 19 th -century House acknowledge that an informal "positional leadership" system emerged possibly as early as the "War Hawk" Congress (1811-1813) under Speaker Henry Clay. Under this system, the Speaker—who at the time designated the chairmen of the standing committees—would name his principal lieutenant to be chairman of the Ways and Means Committee. After the Appropriations Committee was split from the Ways and Means Committee in 1865, the Speaker's principal floor lieutenant received either of these chairs. Sometimes, the Speaker chose a rival for the speakership to chair one of these committees in an effort to resolve intra-party disputes. It is somewhat inaccurate, however, to consider these early leaders to be majority leaders in the modern sense, and they have not been included here. The position of chair of the Appropriations or Ways and Means Committee inevitably made the incumbent a powerful congressional figure because of the important legislation reported from these committees. These chairs were not, however, chosen in a vote by the full party organization, as the majority or minority House leaders are now. Furthermore, other leading congressional figures, such as the Republican leader Thomas Brackett Reed, achieved their positions of influence within the House by service on other committees, such as—in Reed's case—the post-1880 Rules Committee. The Senate developed an identifiable party leadership later than the House. The few existing records of party conferences in the 19 th -century Senate are held in private collections. Memoirs and other secondary sources reveal the identities of party conference or caucus chairs for some, but not all, Congresses after about 1850; these posts, however, carried very little authority. It was not uncommon for Senators to declare publicly that within the Senate parties there was no single leader. Instead, through the turn of the 20 th century, individuals who led the Senate achieved their position through recognized personal attributes, including persuasion and oratory skills, rather than the current practice of election to most official leadership posts. The development of Senate party floor leaders was one of slow evolution, like the House, but they arose for the most part from the post of conference chair. Not until 1945 did Senate Republicans specify that the conference chair and floor leader posts must be held by separate Senators. Among Senate Democrats, the floor leader is also chair of the conference. In many secondary sources, Senators are identified as "floor leaders" before existing party conference records so identify them. In this report, footnotes to the tables attempt to clarify when a leader was identified through official sources such as caucus minutes or through secondary sources. Another problem in identifying party leaders in early Congresses is the matter of party affiliation. Secondary sources reporting on party leaders often relied upon the information compiled in early editions of the Biographical Directory of the United States Congress . As the editors of the 1989 edition of the Biographical Directory noted: The most serious source of error and confusion in previous editions [of the Biographical Directory ] [was] the designations of party affiliation. Many of the party labels added to the editions of 1913 and 1928 were anachronistic, claiming for the two modern parties Senators and Representatives elected to Congress before the [modern] Democratic or Republican parties existed. Other entries ignored the frequent shifts in party affiliation during the nineteenth century or omitted reference to short-lived and regional political parties and thus failed to reflect the vigor and diversity of nineteenth-century politics. The 1989 and 1997 editions of the Biographical Directory resolved these differences, and their designations of party affiliations are principal sources for this report. The 1997 edition of the Biographical Directory , in particular, included more complete notations where Members changed their party affiliations while serving in Congress. The main source for early party affiliations of Senator leaders, principally Presidents pro tempore, is volume four of Senator Robert C. Byrd's The Senate, 1789-1989 (Historical Statistics, 1789-1992) . An Appendix explains the abbreviations used to denote party affiliations in this report. The tables in this report exclude some leadership posts in order to render manageable the amount of data provided. Specifically, the Senate and House party conference secretaries and the chairs of party committees (e.g., steering committees, policy committees, committees on committees, and campaign committees) are not presented here. Junior party whips are also not identified. At least since the 1930s in the House, both parties have selected (or allowed the principal whip to designate) subordinate whips. The lack of adequate records makes it almost impossible to identify all deputy whips, regional whips, and zone whips who have been appointed in the past 70 years. The position of Speaker is constitutionally specified in Article 1, Section 2. The Speaker is the only party leader who is chosen by a roll-call vote of the full House of Representatives, which occurs after each party has nominated a candidate for the position when a new Congress convenes. House rules give the Speaker various formal duties. These include, for example, administering the oath of office to new Members, signing House-passed bills and resolutions, presiding over the House (and making rulings on the presence of a quorum, points of order, etc.), referring measures to committees, and naming the party's slate of members for certain committee positions. Each party conference cedes additional powers and responsibilities to a Speaker from its own party, including influence over the makeup of certain standing committees. For more information, consult CRS Report 97-780, The Speaker of the House: House Officer, Party Leader, and Representative , by [author name scrubbed], and CRS Report RL30857, Speakers of the House: Elections, 1913-2017 , by [author name scrubbed] and [author name scrubbed]. At an organizational meeting prior to the beginning of a new Congress, each party conference (or caucus) in the House selects its floor leader (also called majority leader or minority leader, as appropriate) in a secret-ballot vote. The majority party floor leader works closely with the Speaker and is largely responsible for the party's daily legislative operations in consultation with other party leaders. Similarly, the minority party floor leader directs the party's ongoing legislative strategies and operations and typically serves as the spokesperson for the party in the House. Each party assigns additional responsibilities to its respective floor leader. For more information on the majority party floor leader position, see CRS Report RL30665, The Role of the House Majority Leader: An Overview , by [author name scrubbed]. Each House party caucus currently elects its own party whip at organizational meetings as a new Congress begins. House Republicans (or a representative group of their conference) have always elected their party whips; Democrats in the House appointed a chief whip until 1986. Chief deputy whips are currently appointed by the party's chief whip; additional members to serve in the whip team are either similarly appointed or, instead, elected by subsets of the caucus. The whip organization is responsible for assessing the passage prospects for upcoming measures, mobilizing member support for leadership priorities, informing the party rank-and-file regarding legislative scheduling and initiatives, and informing the top party leadership regarding the sentiment of the rank-and-file. For more information, see archived CRS Report RS20499, House Leadership: Whip Organization , by [author name scrubbed]. The Republican Conference and the Democratic Caucus are the organizations of the members of the respective parties in the House. Each conference has an elected chair, who presides over its meetings. Decisions made by the conference (and often publicly promulgated by the chair) are generally regarded as the collective sentiment of the respective House party contingent. Pursuant to Article 1, Section 3, of the U.S. Constitution, the President pro tempore of the Senate is the chamber's presiding officer in the absence of the President of the Senate (the Vice President of the United States). The President pro tempore is elected by the full Senate as the formal institutional leader and, in current practice, is the longest-serving member of the majority party. Until 1890, the Senate elected a President pro tempore whenever the Vice President was not in attendance, whether for a day or permanently, as in the case of the Vice President's death or resignation. When the Vice President returned, the President pro tempore lost his place. When the Vice President was again absent, the Senate again elected a President pro tempore—in many cases the same Senator who had been chosen before. By the standing order agreed to on March 12, 1890, the Senate declared that the President pro tempore shall hold the office during "the pleasure of the Senate and until another is elected, and shall execute the duties thereof during all future absences of the Vice President until the Senate does otherwise order." The Senate's President pro tempore is, pursuant to statute, currently third in the line of presidential succession (behind the Vice President and the Speaker of the House). In the Succession Act of 1792, the position was initially designated to serve in line after the Vice President. An 1886 act altered the succession line by replacing congressional leaders with cabinet secretaries, but the President pro tempore post was reinstated in the line (in the current position) in 1947. As presiding officer, the President pro tempore has the power to decide points of order and enforce decorum on the floor. The President pro tempore has other formal powers (e.g., appointing conferees; appointing certain Senate officers; and serving on, or appointing others to, working groups, commissions, and advisory boards). However, because the direction of Senate business has fallen in modern times to the majority leader, almost all of these powers are actually exercised by the majority leader in practice. As explained in the notes to Table 9 and Table 10 below, the Senate has also had past occasion to select a Deputy President pro tempore and a Permanent Acting President pro tempore. For more information on the President pro tempore (and the deputy and acting posts), consult CRS Report RL30960, The President Pro Tempore of the Senate: History and Authority of the Office , by [author name scrubbed]. The Senate has, on occasion, created special offices connected to the position of President pro tempore. These two positions—detailed below—were created for specific individuals under narrow circumstances and are not currently in use. Pursuant to S.Res. 17 (95 th Congress), agreed to January 10, 1977, the Senate established (effective January 5, 1977) the post of Deputy President pro tempore of the Senate to be held by "any Member of the Senate who has held the Office of President of the United States or Vice President of the United States." Senator Hubert H. Humphrey was Deputy President pro tempore until his death on January 13, 1978. In the 100 th Congress, due to concerns over the health of the President pro tempore, Senator John S. Stennis, the Senate agreed on January 28, 1987, to S.Res. 90 , authorizing the Senate to designate a Senator to serve as Deputy President pro tempore during that Congress in addition to Senators who hold such office under the authority of S.Res. 17 (95 th Congress). Accordingly, on the same date, the Senate agreed to S.Res. 91 (100 th Congress), designating Senator George H. Mitchell Deputy President pro tempore. This post was initially established in 1963 after Senate Majority Leader Michael J. Mansfield became concerned that the stamina of then-President pro tempore Senator Carl T. Hayden would be overly taxed by presiding over the prolonged debate on civil rights legislation. In response, the Senate adopted S.Res. 232 and S.Res. 238 (88 th Congress), making Senator Lee Metcalf Acting President pro tempore from December 9, 1963, until the meeting of the second session of the 88 th Congress. Continuing concerns over the presiding officer's responsibilities led the Senate, on February 7, 1964, to authorize Senator Metcalf "to perform the duties of the Chair as Acting President pro tempore until otherwise ordered by the Senate" via S.Res. 296 (88 th Congress). Senator Metcalf held the post throughout his remaining 14 years in the Senate. Each Senate party conference selects its floor leader (also called majority leader or minority leader, as appropriate) in a secret-ballot vote at its organizational meeting prior to the beginning of a new Congress. While these positions developed later than (and arose from) the post of conference chair, they now represent the top post in each party. The majority leader is the lead spokesperson for the party in the chamber and is also responsible for scheduling the legislative activity of the Senate. By precedent established in 1937, the majority leader is afforded priority recognition on the floor. The minority leader leads and speaks for the minority party and is consulted by the majority leader in scheduling Senate floor activity; he also has preferential floor recognition, after the majority leader. The rules of each party conference assign additional responsibilities to each floor leader, as well. In current practice, the floor leader for Senate Democrats also serves as the party's conference chair. (See next section for description of conference chair positions.) Each party has a conference organization consisting of all the elected Senators from that party; it is the main body through which the party contingent at large decides and communicates its legislative priorities. While each party's conference chair posts were the first formal party leadership positions in the Senate, eventually floor leader positions were established as uppermost in each party's leadership hierarchy. Since 1945, Republicans have elected their conference chairs separately from other leadership posts, but the elected Democratic floor leader also serves as chair of the Democratic Conference. (See Table 12 for the list of Democratic floor leaders/conference chairs.) Senate Democrats first selected a party whip in 1913; Republicans followed in 1915. Some accounts of these early selections imply that the individuals were initially appointed, but other contemporary accounts refer to conference elections for the posts. (Republicans first formally codified their conference procedures in 1944, making it clear that the whip post was elected by the conference.) Today, each party conference elects a party whip (sometimes called the assistant majority leader or assistant minority leader, depending on the party). Typically, deputy whips are also appointed to assist the whip operation. The whips communicate leadership priorities to the party rank-and-file (and vice versa), provide leaders an assessment of member support for (or opposition to) pending legislative matters, and mobilize support for leadership-supported measures under consideration. For more information, see archived CRS Report RS20887, Senate Leadership: Whip Organization , by [author name scrubbed]. This report relies heavily on primary congressional sources and authoritative documents such as the privately printed Biographical Directory of the American Congress, 1774 to 1996 , and a similar online adaptation, the Biographical Directory of the United States Congress, 1774 to the Present . In addition, over the years, individual Members of Congress, legislative aides, and scholars have gained limited access to party conference journals. Reliable leadership lists have been compiled from these sources. Where these have been published, they have been used as a source in this report. This report also relies on secondary sources developed by scholars. The Congressional Research Service made no attempt to gain access to caucus or conference minutes in collecting data for this report. Inevitably, conflicting interpretations occur in these data, even among sources generally accepted as reliable. For example, there are disparities on the dates of elections and tenure of Senate Presidents pro tempore among Byrd's history, the 1911 Senate document, and Gamm and Smith's research. The report attempts to footnote these divergences where they occur. Unless otherwise noted, the following sources were used to compile the tables in this report: Berdahl, Clarence. "Some Notes on Party Membership in Congress." American Political Science Review , vol. 43 (April 1949), pp. 309-332; (June 1949), pp. 492-508; and (August 1949), pp. 721-734. Biographical Directory of the American Congress , 1774-1996 . Washington: CQ Staff Directories, Inc., 1997. Biographical Directory of the United States Congress, 1774 to the Present. Available at http://bioguide.congress.gov/biosearch/biosearch.asp . Byrd, Robert C. The Senate, 1789-1989 . 4 vols., 100 th Congress, 1 st session. S. Doc. 100-20. Washington: GPO, 1988-1993. Cannon, Clarence. "Party History." Remarks in the appendix, Congressional Record , vol. 89 (January 22, 1941), pp. A383-A384. Congressional Directory . Washington: GPO, various years. Congressional Globe . Washington, 1833-1873. Congressional Quarterly Weekly Report . Washington: Congressional Quarterly, Inc., various dates. Congressional Record . Washington: GPO, 1873-present. CRS Report RL30960, The President Pro Tempore of the Senate: History and Authority of the Office , by [author name scrubbed]. Deschler, Lewis. Deschler-Brown Precedents of the United States House of Representatives. 16 vols. Washington: GPO, 1977-2000. Galloway, George B. "Leadership in the House of Representatives." The Western Political Quarterly , vol. 12, no. 2, (June 1959), pp. 417-441. Gamm, Gerald and Steven S. Smith. "Last Among Equals: The Senate's Presiding Officer." In Burdett A. Loomis, ed., Esteemed Colleagues: Civility and Deliberation in the U.S. Senate , pp. 105-134. Washington: Brookings Institution Press, 2000. Martis, Kenneth C. The Historical Atlas of Political Parties in the United States Congress, 1789-1989. New York: Macmillan, 1989. Oleszek, Walter J. Majority and Minority Whips in the Senate : History and Development of the Party Whip System in the U.S. Senate . 99 th Congress, 1 st session. S. Doc. 99-23. Washington: GPO, 1985. ——. "John Worth Kern: Portrait of Floor Leader." In Richard A. Baker and Roger H. Davidson, eds., First Among Equals: Outstanding Senate Leaders of the Twentieth Century , pp. 7-37. Washington: CQ Press, 1991. Ripley, Randall B. Party Leaders in the House of Representatives. Washington: Brookings Institution Press, 1967. ——. "The Party Whip Organizations in the United States House of Representatives." American Political Science Review , vol. 58 (September 1964), pp. 561-576. Rothman, David J. Politics and Power . Cambridge, MA: Harvard University Press, 1966. U.S. Congress. Hinds' and Cannon's Precedents of the House of Representatives of the United States . 11 vols. Washington: GPO, 1907-1908, 1935-1941. ——. House. Journal of the House of Representatives of the United States , 1789-present, various publishers. ——. Senate. Journal of the Senate of the United States , 1789-present, various publishers. ——. Majority and Minority Leaders of the Senate: History and Development of the Offices of the Floor Leaders . Prepared by Floyd M. Riddick. 99 th Congress, 1 st session. S. Doc. 99-3. Washington: GPO, 1985. ——. President of the Senate Pro Tempore . 62 nd Congress, 2 nd session. S.Doc. 62-101. Washington: GPO, 1911. Widenor, William C. "Henry Cabot Lodge: The Astute Parliamentarian," In Richard A. Baker and Roger H. Davidson, eds., First Among Equals: Outstanding Senate Leaders of the Twentieth Century , pp. 38-62. Washington: CQ Press, 1991.

Summary: This report briefly describes current responsibilities and selection mechanisms for 15 House and Senate party leadership posts and provides tables with historical data, including service dates, party affiliation, and other information for each. Tables have been updated as of the report's issuance date to reflect leadership changes. Although party divisions appeared almost from the First Congress, the formally structured party leadership organizations now taken for granted are a relatively modern development. Constitutionally specified leaders, namely the Speaker of the House and the President pro tempore of the Senate, can be identified since the First Congress. Other leadership posts, however, were not formally recognized until about the middle of the 19th century, and some are 20th-century creations. In the earliest Congresses, those House Members who took some role in leading their parties were often designated by the President as his spokesperson in the chamber. By the early 1800s, an informal system developed when the Speaker began naming his lieutenant to chair one of the most influential House committees. Eventually, other Members wielded significant influence via other committee posts (e.g., the post-1880 Committee on Rules). By the end of the 19th century, the formal position of floor leaders had been established in the House. The Senate was slower than the House to develop formal party leadership positions, and there are similar problems in identifying individual early leaders. For instance, records of party conferences in the 19th century Senate are not available. Memoirs and other secondary sources reveal the identities of party conference or caucus chairs for some, but not all, Congresses after about 1850, but these posts carried very little authority. It was not uncommon for Senators to publicly declare that within the Senate parties, there was no single leader. Rather, through the turn of the 20th century, individuals who led the Senate achieved their positions through recognized personal attributes, including persuasion and oratorical skills, rather than election or appointment to formal leadership posts. The formal positions for Senate party floor leaders eventually arose from the position of conference chair. Owing to the aforementioned problems in identifying informal party leaders in earlier Congresses, the tables in this report identify each leadership position beginning with the year in which each is generally regarded to have been formally established. The report excludes some leadership posts in order to render the amount of data manageable. A bibliography cites useful references, especially in regard to sources for historical data, and an appendix explains the abbreviations used to denote political parties. This report will be updated as changes in House and Senate party leadership positions occur.