Boldface (with superscript C) numbers indicate the majority Party in each house. Red (with superscript P) numbers (boldface or not) indicate the Party of the President in any event.

The political breakdown of each Congress as it appears on the above chart is that of the division of each house of Congress among the Parties "as elected"- that is, it reflects the sum total of the number of seats won by the Parties as solely determined by the winners of the election for each seat in each house of Congress in a regular General election for a given Congress (or, in the Senate only, a Special Election held on the same date or soon enough after the regular, General Election [provided said Special Election takes place prior to the beginning of the terms of those elected to that incoming Congress]). It is intended that the political breakdown of the Parties in a particular Congress for purposes of this chart be determined, as closely as is practicable, by the "intention of the electors" ("electors" seen here as starting with a small 'e' to distinguish these from the Presidential Electors of the Electoral College: "electors" in this case means those who have done the actual choosing of United States Senators and Representatives in Congress- the voters in each State or Congressional District [and, prior to the effectiveness of the 17th Amendment to the United States Constitution in 1913, the members of the State Legislatures electing their States' U.S. Senators]).

A few general considerations...

Throughout pretty much the entire history of the House of Representatives, as well as in the United States Senate since the 64th Congress (as a result of the aforementioned 17th Amendment, which provided for popular election of the Senators from each State), some person has always been elected to a given seat in either house in a General Election- even should that seat be contested or that person predecease the incoming Congress to which he or she has been elected (or, perhaps, even be elected after having already died, as was the case in the election for a U.S. Senate seat from Missouri in 2000). As a result, there is no column provided for vacancies in that portion of the above chart relating to the House of Representatives, since- theoretically- a regular General Election (however disputed the results of same might turn out to be) has always been held- every two years- for every seat in that body: even for seats which may, in fact, turn out to have been vacated by the time the Congress has actually convened, met and/or organized following said election.

This same situation as generally regards the House would also hold true for the United States Senate since the 64th Congress: that is, there would- under normal circumstances- be no true "vacancies" in the Senate from the General Election of 1914 on, as- at least in theory- someone has always been elected to a Senate seat in such a regular General Election ever since that date. Such General Election results for the House throughout its history and the Senate since the implementation of the 17th Amendment (even where the apparent Election Night winner of a seat is later denied that seat for any of a variety of reasons) would, by definition, best reflect the "intention of the electors" as to which Party was to, under ordinary circumstances, hold how many seats as a result of the regular General Elections for those seats; accordingly, the numbers seen in the above chart reflect this ideal.

Issues re: the UNITED STATES SENATE into the 63rd Congress (1913)...

Up through the 63rd Congress, however, the United States Senate, in particular, has caused often considerable difficulties in best determining "intention of the electors" by providing- during the period leading up to the convening of said 63rd Congress in 1913- what amounts to a special exception to what has been written in the previous paragraphs, as- again- it was the Legislatures of the several States which were responsible for the regular "General Election" of Senators prior to the ratification of the 17th Amendment: therefore, insofar as this chart is concerned, "as elected" refers to those Senators who had been elected for a particular Senate seat on or before the Saturday immediately preceding the first Monday in December of the odd-numbered year in which the terms of those serving in a given Congress had begun on the 4th of March immediately preceding. The verbiage within the previous sentence might well have been more than a bit confusing, so herewith an explanation:

The only mention, in the original text of the Constitution of the United States, regarding an actual date in relation to the assembling of each Congress is as follows:

The Congress shall assemble at least once in every Year, and such Meeting shall be on the first Monday in December, unless they shall by Law appoint a different Day. [Article I, Section 4, clause 2]

The debate on the floor of the 1787 Constitutional Convention in Philadelphia regarding this provision (and there was not all that much discussion, to be sure) suggests that this particular date for the convening of Congress- the first Monday in December- was chosen because it, at the time, appeared to be the most convenient (given the transportation technology and infrastructure available to late 18th Century America) in relation to the various dates for Election Day in most, if not all, of the 13 original States as set in the State' own Constitutions and/or Laws; this implies that it might well also have been intended by the Framers to be the beginning date for terms of U.S. Senators and Representatives in Congress but for the fact that the dying Confederation Congress, in the course of setting the schedule for the first Presidential Election and the convening of the 1st Congress in the wake of ratification of the new Federal Constitution, later decided that the new Federal Government could effectively take over from the Confederation on the first Wednesday in March, 1789 (which happened to be 4 March that year, a date which, ever after- at least until the adoption of the 20th Amendment in 1933, determined the beginning of the terms of Senators and Congressmen). Thus, from the very start of American federal governance, there was a nine month (give or take) discrepancy between the date the terms of members of a given Congress began and the date stated in the Constitution as to when said Congress was actually to convene!

As a result of this discrepancy, it was always rather possible for a State's legislature (especially one that was not scheduled to itself convene until well into the odd-numbered year [limited biennial sessions (one legislative session every two years, with limits as to its length) being far more common than nowadays]) to not actually choose a Senator (whether this be a regular election for a full six-year term or a Special Election to fill a vacancy in the midst of a six-year term) until after- in some cases, well after- the 4 March in that same odd-numbered year on which the term of the Senator-yet-to-be-chosen was to have begun. For the purposes of the above chart, therefore, it is presumed that a Senator elected in a regular election to a full six-year term is not to be counted in the political party breakdown unless that person was chosen by his State's legislature on or before the Saturday immediately preceding the first Monday in December on which Congress was, under normal circumstances, constitutionally required to assemble (the theory here is that, in the America of 1789 through 1913, no legislature would meet on a Sunday- it being the universal [Christian] day of rest- so that this Saturday would be the latest a Senator could be elected and still, if only theoretically [until towards the end of this period, when better transportation to the Nation's Capital- such as the railroads- became available], be eligible to be sworn into Congress on or before the first Monday in December of the odd-numbered year).

The same issue might also affect a Special Election in which a State's legislature was (prior to 1913, obviously) called upon to choose a person to fill a vacancy in the Senate: if said Special Election was held on or before the Saturday immediately preceding the first Monday in December of an odd-numbered year, then the political party of the person chosen to fill the vacancy is the one counted in the above chart: otherwise the political party of the person replaced in the Special Election is that which is counted (so long as that person was still serving as a Senator on 4 March of that same odd-numbered year, of course). In any case where no one had been elected to the full six-year term re: a given Senate seat- or where a Senator had already vacated a given Senate seat through death or resignation- by 4 March of an odd-numbered year and no successor to the same seat was to have been elected by the affected State's legislature by the Saturday immediately preceding the ensuing first Monday in December, only then is the Senate seat considered to have been vacant for purposes of the above chart; for this reason, a column is provided- in the portion of the above chart relating to the United States Senate- for vacancies.

Issues re: the U.S. HOUSE OF REPRESENTATIVES through the 45th Congress (1878)...

In addition, many more difficulties in determining "intention of the electors" are provided by the once-common practice of many States holding their regular, General Elections to the House of Representatives in odd-numbered years, perhaps even after a particular Congress had already officially begun its term of office on the 4th of March in that same odd-numbered year (yet still before that Congress was actually to first convene no later than the first Monday in December following, as required in that same Article I, Section 4, clause 2 of the U.S. Constitution quoted earlier); this practice of odd-year General Elections to the House was not finally abandoned altogether until the Elections of 1878 (due to a series of Federal statutes, passed during the course of the 1870s, which came to require that all popularly-elected members of Congress must be "regularly elected" [as opposed to "specially elected"- that is, in a General Election as opposed to a Special Election to fill a vacancy] on the first Tuesday after the first Monday in November of the even-numbered year next preceding the odd-numbered year in which the given Congress to which such members were being elected was to take office (on 4 March, until- again- the 20th Amendment changed that date to the 3 January beginning with the 74th Congress in 1935).

Thus, through the 45th Congress, "as elected"- for the purposes of the above chart- refers to any Congressmen elected in any regular, General Election for a given Congress (but, please note, not Special Elections to fill vacancies in seats for which someone had already been elected to that Congress- even where such a Special Election in one State may actually have, in fact, predated the General Election for the House in another State) so long as that General Election was held prior to the Saturday immediately preceding the first Monday in Decmber in an odd-numbered year (on a theory similar to the reason for the use of this admittedly arbitrary date re: the Senate-- no election would have been held on a Sunday [the Christian Sabbath and, hence, the universal day of rest during the period in question] and, therefore, the latest anyone could have been elected to Congress in time to, however theoretically, be sworn in as a member of the U.S. House of Representatives on the date constitutionally set aside for the annual convening of Congress would have been the preceding Saturday).

Some final thoughts...

All in all, the political breakdown of Congress as seen in the above chart may, at least from time to time, reflect what might best be considered as a "theoretical" model of the numerical relationship of the political parties to each other in each Congress rather than the actual breakdown of Political Parties in a given Congress at any specific time; that is, it is best that the chart above be taken as merely a guide to the political breakdown of Congress as intended by those who chose its members at whatever time it happened to choose them instead of its being seen as an actual tabulation of how many bodies from what Party actually filled seats in either house of Congress!

The reason for this is that it is the considered opinion of the Staff of 'The Green Papers' that the only fair way to compare any election to another is to compare the results of one election to the results in another (rather than comparing the results of a given election to how many persons from each political party happened to be serving in either house of Congress on the eve of that election [for the numbers re: each party might well be significantly different by then than those gleaned from the preceding election]): the "rules"- as stated above- for dealing with the United States Senate up through 1913 and the U.S. House of Representatives prior to the 1878 elections are an attempt to mathematically make Congresses whose members- re: both houses- were, in that long ago past, chosen in rather different manners than these same elected officials are chosen today that much more comparable to the more recent congressional elections.

It should also here be noted that a Senator having officially changed his political Party in the midst of his or her term of office is not at all recognized in the above chart unless and until an election- whether regular or special- of that same person as a candidate of his or her new Party has intervened (thus, for example, Senator Jeffords of Vermont is still counted as a "Republican" in both the 108th and 109th Congresses on the above chart, even though he switched to being an Independent during the 107th Congress: the reason for this is that the intention of the voters who went to the polls in the 2000 election in which he was re-elected was that he be so re-elected as a Republican and that intention cannot be changed simply because the Senator himself has decided to change his Party affiliation on his own). The only exceptions to this rule, as regards the above chart, involve the 19th and 20th Congresses (covering the period 1825-1829)- during which the so-called "old" Republicans split into a pro-Andrew Jackson faction and a pro-John Quincy Adams faction, each of which gave rise to- eventually- the Democratic and the Whig Parties, respectively- and the 34th and 35th Congresses (covering the period 1855-1859)- during which the Whig Party disintegrated and the new Republican Party first emerged as the principal Major Party in opposition to the Democrats: during each of these two exceptional periods (and, in at least some cases, some time thereafter), a Senator elected as a member of a given Party might well have to be counted, later in the same six-year term, as being a member of a different Party without an intervening election as a candidate of that Party... but it should be noted that these two periods in question were, indeed, exceptional within the general stream of American political history.

In addition: none of what has been noted in the previous paragraph applies at all to members of the U.S. House of Representatives, since there is a new General Election for all members of that chamber every two years and any changes of Congressmen from one Party to another (whether during those two historically exceptional periods in question or not) between Congresses will always be noted as a matter of course as flowing from the summation of the results of each and every congressional election!

Modified .