Presiding Officer of the United States Senate

During the 20th century, the role of the vice president evolved into more of an executive branch position.

In actual practice in the modern Senate, the president pro tempore also does not often serve in the role (though it is their constitutional right to do so).

From John Adams in 1789 to Richard Nixon in the 1950s, presiding over the Senate was the chief function of vice presidents, who had an office in the Capitol, received their staff support and office expenses through legislative appropriations, and rarely were invited to participate in cabinet meetings or other executive activities.

In 1961, Vice President Lyndon B. Johnson changed the vice presidency by moving his chief office from the Capitol to the White House, by directing his attention to executive functions, and by attending Senate sessions only at critical times when his vote, or ruling from the chair, might be necessary.

As a result, the Senate frequently elected several presidents pro tempore during a single session.

[2] On three occasions during the 19th century, the Senate was without both a president and a president pro tempore: Additionally, Article One, Section 3, Clause 6 grants to the Senate the sole power to try federal impeachments and spells out the basic procedures for impeachment trials.

Among the requirements is the stipulation that the Chief Justice of the United States is to preside over presidential impeachment trials.