Article I, Section 3 of the Constitution sets up the United States Senate and gives it the sole power to try impeachments. It fixes the number of senators from each state, the length of their terms, who qualifies to serve, who presides over the chamber, and what happens when a federal official faces removal from office.
Two Senators From Each State
Every state gets two senators, and each senator has one vote. That equal representation was the framers’ answer to the House, where seats are apportioned by population. It puts small states and large states on the same footing in the upper chamber.
The original text had state legislatures choose senators. That method held until 1913, when the 17th Amendment moved the choice to the voters. The change followed decades of legislative deadlocks that left seats empty for months and corruption scandals in several states. The two-per-state structure stayed; only the selection method changed.
Six-Year Terms and Three Classes
Senators serve six years, three times a House term. The framers treated the longer term as a stabilizing feature, letting senators work on policy without a two-year election clock.
To keep the whole chamber from turning over at once, the Constitution splits senators into three classes. The first class first stood for election after two years, the second after four, the third after six. Since then, roughly a third of the Senate is up every two years, and two-thirds of the membership carries over from the prior Congress.
How Senate Vacancies Are Filled
When a seat opens mid-term, the 17th Amendment requires the state’s governor to call a special election. It also lets a state legislature authorize the governor to appoint someone on a temporary basis until voters decide. Most states have passed such laws, though the details vary from state to state.
Who Qualifies to Serve as a Senator
The Constitution sets three minimum requirements:
- At least 30 years old. Since 1935, the Senate has read this to mean the person must meet the age requirement by the time they take the oath, not necessarily on election day.
- A U.S. citizen for at least nine years, two years longer than the requirement for House members.
- An inhabitant of the state they represent at the time of election. The Constitution sets no minimum time period for living there.
One further bar sits outside Section 3 but works alongside it. Section 3 of the 14th Amendment disqualifies anyone who previously swore an oath to support the Constitution as a federal or state official and then engaged in insurrection or rebellion against the United States. It does not require a criminal conviction. Congress can lift the disqualification only by a two-thirds vote of both chambers.
Who Presides Over the Senate
The Vice President of the United States is President of the Senate. The Vice President has no regular vote and may vote only to break a tie.
Because the Vice President is rarely on the floor, the Constitution directs the Senate to elect a President pro tempore to preside in the Vice President’s absence. That officer is a sitting senator with full voting rights and the ability to debate. By tradition, the role goes to the longest-serving member of the majority party. Under federal succession law, the President pro tempore stands in line to act as President if the presidency and vice presidency are both vacant and no Speaker of the House is able to serve.
The Senate’s Power to Try Impeachments
The House impeaches; only the Senate tries the case. Every senator must be placed under oath before the proceedings begin. When the President of the United States is on trial, the Chief Justice of the United States presides, not the Vice President, who would stand to benefit from a conviction.
Conviction requires a two-thirds vote of the senators present. That threshold has been hard to reach. Of the 22 impeachment trials the Senate has conducted since 1789, only eight ended in conviction, all of them federal judges. No president has been convicted.
What Happens After a Conviction
The Constitution caps the penalty at two things: removal from office and disqualification from holding future federal office. They are not one automatic package. Removal follows conviction immediately. Disqualification is a separate question the Senate may take up afterward, and it needs only a simple majority rather than two-thirds.
Impeachment is political, not criminal. A convicted official can still be indicted, tried, and punished in the regular courts. The Senate’s judgment strips someone of office; it does not settle criminal liability.