During a time of badly strained relations between the president of the Senate's majority party, senators adopted a rule of requiring referral of all nominations to committee prior to consideration by the full Senate. At the same time, President Andrew Johnson's decision to remove from office Secretary of War Edward Stanton, which angered the majority of Republicans, prompted the Senate to adopt a resolution denying the president such power without the consent of the Senate. Three days later, the House of Representatives impeached Andrew Johnson. On May 16, 1868, the Senate acquitted the president by falling one vote short of the required two-thirds majority to convict.

Vice President John Adams led the entire Senate in a visit to President George Washington to offer congratulations on his 59th birthday. Decades later, on February 22, 1862, as a morale-boosting gesture during the darkest days of the Civil War, the Senate and House of Representatives met in a joint session to hear Secretary of the Senate John W. Forney read Washington's famous 1796 farewell speech. Twenty-six years later, on February 22, 1888, the Senate began an annual tradition that continues today. Each year, on or near the first president's birthday, a senator reads Washington's Farewell Address in the Senate Chamber.

Senator Alben Barkley (D-KY) resigned his post as majority leader after President Franklin Roosevelt vetoed a tax bill against Barkley's advice. The majority leader charged that the president's characterization of the bill as tax relief for the greedy was a "calculated and deliberate assault on the legislative integrity of every member of Congress." Following Barkley's "farewell" speech, the Senate gave him a boisterous standing ovation. Within minutes of receiving his letter of resignation, the conference of Democratic senators unanimously reelected him as their leader. Barkley served 12 years as Democratic floor leader, from 1937 to 1948, when he became vice president.

The Senate instructed its sergeant at arms to ban all flowers from the Senate Chamber. One newspaper, describing the House of Representatives Chamber on the first day of a new session in 1900, noted "the profusion of floral pieces gave the vast hall more the appearance of a garden than a legislative assembly....The air was so laden with perfume as to be a degree unpleasant." Not surprisingly, floral tributes from hopeful lobbyists ended up on the desks of committee chairmen and other senior members. This aroused suspicion that junior senators, not to be left out, arranged for their own displays.

Hiram R. Revels (R-MS) took the oath as a United States senator, thus becoming the Senate's first African American member. Born in North Carolina in 1827, Revels attended Knox College in Illinois and later served as minister in the African Methodist Episcopal Church in Baltimore, Maryland. He raised two black regiments during the Civil War and fought at the battle of Vicksburg in Mississippi. Elected to the Senate by the Mississippi state legislature, Revels became an outspoken opponent of racial segregation. Although Revels served only one year in the Senate, he broke new ground for African Americans in Congress.

When the Senate opened its first permanent office building in 1909—now known as the Russell Building—Congress authorized construction of a subway to carry senators from the Capitol to their offices. The subway was not a railroad, but rather a pair of lemon-yellow, battery-powered buses made by Studebaker. The high, four-wheeled coaches carried eight passengers, whose heads narrowly cleared the tunnel's low ceiling. When a second office building—the Dirksen Building— opened in 1958, the subway line was extended and modernized. In 1983 the newest office Building—Hart— required one more extension. Today, the busy underground system serves the entire Senate complex.