Classification of Senators.—The Constitution provided that immediately upon the assembling of the senators after the first election they should be divided into three classes and that the seats of those in the first class should be vacated at the end of the second year, those of the second class at the expiration of the fourth year, and those of the third class at the expiration of the sixth year, so that thereafter one third might be chosen every second year. The purpose of this provision is to avoid having the entire senate renewed at the same time. As a result, not more than one third are new and inexperienced members at any particular time. When a new state is admitted to the Union, its first two senators draw lots to see which class each shall fall in. In 1921 there were thirty-two senators in the first class, and their terms expire March 4, 1923; thirty-two in the second class, and their terms expire March 4, 1925; and thirty-two in the third class, and their terms expire March 4, 1927. The three classes are kept as nearly equal as possible.

Reëlection of Senators.—While the term of a senator is six years, he may be reëlected as often as his state may see fit to honor him, and in practice reëlections have been frequent. Justin S. Morrill of Vermont, John Sherman of Ohio, and William B. Allison of Iowa, each served continuously for a period of thirty-two years. Nearly one third of the senators in 1911 had served twenty years or more. Thus the senate is an assembly of elder statesmen and is a more conservative and stable body than the house of representatives.

Mode of Election of Senators.—In regard to the mode of election of senators there was a wide difference of opinion among the members of the convention. Some favored choice by the people; others favored election by the lower house of Congress; some proposed appointment by the President from persons nominated by the state legislatures; while others proposed election by the state legislatures, which was the method finally agreed upon. Choice by the legislature, it was felt, would be the means of forming a connecting link between the state governments and the national government and would thereby tend to attach the former to the latter—an important consideration then, in view of the prevailing jealousy of the state governments toward the national government. Finally, it was believed that choice by the legislature would tend to secure the election of senators of greater ability since the members of the legislature would be more familiar with the qualifications of candidates than the masses of the people could hope to be.

Objections to the Method of Choice by the Legislature.—One of the practical objections to the original method of choosing senators was that it frequently led to long and stubborn contests which sometimes ended in deadlocks. Not infrequently the legislature failed to elect a senator and the state was left with a vacancy in the senate. In such cases the governor could not fill the vacancy by appointment as he did when a senator died or resigned; the seat remained vacant until a senator was chosen by the legislature. From 1890 to 1912 not less than eleven states at one time or another were represented in the senate by one member only, and in 1901 Delaware, on account of repeated deadlocks, had no senator at all at Washington to speak for the state. Not infrequently such contests were broken through the selection of a second-rate man or by an alliance between the members of the minority party and certain members of the majority.

Bribery.—The breaking of deadlocks was sometimes accomplished by bribery or other improper influences. Indeed charges of bribery and corruption in connection with the election of senators came to be very common, and there is little doubt that between 1895 and 1910 a number of wealthy men found their way into the senate through the votes of legislators who were liberally paid for their support. Under these circumstances it was frequently said that the senate was no longer truly representative of the interests of the people.

Interference with Legislative Business.—A prolonged senatorial contest also interfered too much with the regular business of the state legislature. Where the session is limited to two or three months, as it frequently is, the inroads upon the time at the disposal of the legislature for looking after the needs of the state were considerable.[28] Members were badgered by candidates, passions and animosities were engendered, a party coloring was given non-partisan measures, and the votes of members on legislative measures were sometimes determined by the senatorial contest, rather than by the merits of the measure on which they were called to vote.

Popular Election of Senators.—The dissatisfaction with the old method of choosing senators led to a movement to secure an amendment to the Constitution providing for the election of senators by the people. But the senate itself for a long time blocked every attempt of this kind. Five different times between 1893 and 1911 the national house of representatives by a large majority proposed an amendment for this purpose, but each time the senate refused its concurrence. In one form or another the legislatures of thirty-one states approved of the method of popular election and wherever a referendum was taken on the proposition, as was done in California, Nevada, and Illinois, the popular indorsement was overwhelming. Finally, in 1912, the senate yielded, and both houses of Congress adopted a resolution proposing an amendment providing for the popular election of senators, which was ratified by the necessary number of states during the following year. Under this seventeenth amendment the senators of each state are elected by vote of such persons as are entitled to vote for members of the lower house of the legislature.

The seventeenth amendment provides that whenever a vacancy occurs in the senate the governor of the state in which the vacancy occurs shall issue a writ of election for the filling of such vacancy, but that the legislature may authorize the governor to fill the vacancy by a temporary appointment, the appointee to hold until a senator may be chosen by popular election. In practice special elections are rarely called for filling vacancies. In most states the governor makes a temporary appointment, the appointee holding until the next regular election when the people elect his successor.

Qualifications of Senators.—The qualifications prescribed for eligibility to the senate are the same in principle as those required of representatives, though a little different in degree. Thus a senator must be at least thirty years of age, must have been a citizen of the United States for nine years and must be a resident of the state at the time of his election. It was thought that the longer term and higher qualifications would tend to give greater dignity and strength to the upper chamber than would be found in the lower house, and at the same time a higher average of ability.

There is no provision of the Constitution which requires a senator to be a resident of a particular part of the state, but in some states there is a custom that the two senators shall be taken from different sections. Thus in Vermont custom requires that one senator shall come from the section of the state east of the Green Mountains and the other from the west side. Sometimes when there is a large city in the state it is the custom to choose one of the senators from the city and the other from the country. For a long time Maryland did not trust this matter to custom but by law enacted that one of the senators should be an inhabitant of the eastern shore and the other of the western shore.