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].