Congress established the Territory of Missouri and granted its residents the right to vote for a legislature.
The Senate debated the slavery question in new territories and future states and finally agreed to the Missouri Compromise, which admitted Maine as a free state and allowed the Territory of Missouri to draft a constitution and form a state government without restrictions on slavery. The compromise set a geographic line by which the status of slavery would be determined for future states: states to the south of the 36º30’ could permit slavery, while in states to the north of that line, slavery would be prohibited.
David Barton of St. Louis took his oath of office as one of Missouri's first two United States senators. Three days later, on December 6, Thomas Hart Benton of St. Louis presented his credentials and was sworn into office. The two senators then drew lots to determine their class assignments. Barton drew Class 2, with a term to expire on March 3, 1825. Benton drew Class 3, with a term to expire March 3, 1827.
Thomas Hart Benton became chairman of the Senate Committee on Indian Affairs, serving until 1828. He then became chairman of the Senate Committee on Military Affairs (today's Committee on Armed Services), a position he held until 1841 and again from 1845 to 1849.
Senator David Rice Atchison maintained a dubious claim to have assumed the office of president of the United States one day. As the Senate's president pro tempore, he was then second in line of presidential succession behind the vice president. The terms of President James K. Polk and Vice President George M. Dallas expired at noon on March 4, a Sunday, and President-elect Zachary Taylor was not inaugurated until Monday, March 5. Atchison boasted for the rest of his life that he technically became president during that short interim, despite the expiration of his own senate term on March 4.
During heated debate on the Senate floor, Mississippi senator Henry Foote pulled a pistol on Senator Thomas Hart Benton as the physically imposing Benton moved toward him down the center aisle. Foote claimed self-defense, while Hart accused Foote of being an assassin. As tempers cooled, a committee was immediately appointed to look into the disorder and the matter quietly went away.
Senator Thomas Hart Benton took to the Senate floor to give a classic speech in opposition to the Compromise of 1850, which dealt primarily with the issues of slavery and western expansion. Not particularly known as an orator, Benton was nevertheless a major figure in the Senate where he had served for nearly 30 years.
Thomas Hart Benton completed his service in the Senate after a record 29 years, 6 months, and 22 days. Senator Benton's service record would stand for over 40 years until it was surpassed by Ohio's John Sherman in 1894. By 2009, Senator Robert C. Byrd of West Virginia had pushed the record for longest serving senator over the 50-year mark. Benton remains Missouri's second longest-serving senator behind Francis Cockrell of Warrensburg.
Future senator Francis P. Blair of St. Louis was the unsuccessful Democratic vice presidential candidate in the 1868 election. Blair was the running mate of former New York governor Horatio Seymour. They lost the election to the Republican ticket of Ulysses S. Grant and Schuyler Colfax.
Charles D. Drake of St. Louis became chairman of the Senate Committee on Education, (today's Committee on Health, Education, Labor, and Pensions), serving until 1870.
Future senator George Vest of Kansas City, then a lawyer in rural Missouri, gained immortality with a speech delivered to a jury in Warrensburg. Prosecuting the case of a farmer whose dog had been killed by a neighbor, Vest eulogized the dog as "man's best friend." "When all other friends depart, he remains. When riches take wings and reputations fall to pieces, he is as constant in his love as the sun in its journey through the heavens." Vest was elected to the Senate nine years later and served there for 24 years (1879-1903).
Former senator Benjamin Gratz Brown of St. Louis was the unsuccessful Democratic vice presidential candidate in the 1872 election. Brown was the running mate of newspaperman Horace Greeley. They lost the election to the Republican ticket of the incumbent Ulysses S. Grant and Massachusetts senator Henry Wilson.
The Senate resolved the disputed election case of Lewis V. Bogy of St. Louis. Thirteen days after Senator Bogy had initially taken his seat the Senate began an investigation into allegations that Bogy had won his seat through bribery and corruption. The Senate's Committee on Privileges and Elections quickly determined there was a lack of evidence and concluded the matter. Bogy continued to serve in the Senate until his death in 1877.
James Shields of Carrollton won election to Missouri's Class 3 Senate seat. Shields had previously represented both Illinois and Minnesota in the Senate. He is the only Senator to ever have served three different states.
A marble statue of former senator Francis P. Blair and a marble statue of former senator Thomas Hart Benton, both by sculptor Alexander Doyle, were accepted by the Senate as Missouri's contributions to the National Statuary Hall Collection. Blair, a former congressman, Civil War general, and vice presidential candidate, served in the Senate from 1871 to 1873. Benton was one of Missouri's two first senators and served in the Senate for nearly 30 years.
William J. Stone of Jefferson City became chairman of the Senate Committee on Indian Affairs, serving until 1914, when he became chairman of the Senate Committee on Foreign Relations. He led that committee unitl 1918.
Senator Harry S. Truman, who had entered the Senate in 1935, was appointed chairman of the Special Committee to Investigate the National Defense Program, which was created to uncover defense-related waste and corruption during the mobilization prior to World War II. The committee became popularly known as the "Truman Committee" and helped propel Senator Truman to national prominence, the office of vice president, and ultimately, the presidency itself.
Senator Harry S. Truman became the Democratic vice presidential nominee for the 1944 election. Truman was the running mate of incumbent president Franklin D. Roosevelt. They won the general election on November 7, defeating the Republican ticket of New York governor Thomas E. Dewey and future Ohio senator John W. Bricker.
Vice President Harry S. Truman became the 12th senator to become President of the United States following the death of President Franklin D. Roosevelt.
A marble bust of Vice President Harry S. Truman by artist Charles Keck was added to the Senate Vice Presidential Bust Collection. Truman served as a senator from Missouri from 1935 to 1945 and vice president in 1945. The bust was commissioned in 1946 and was modeled for by Truman in the White House while he was president.
Among former senator and president Harry S. Truman's recommendations to the Senate's Special Committee on the Senate Reception Room, which was seeking to identify five outstanding former senators whose portraits would be permanently displayed in that room, were Missouri senators Thomas Hart Benton and George Vest. An outside advisory committee of scholars and public figures ranked Benton in seventh place. Although he wasn't included among the "famous five," the Senate committee recommended that Benton be considered for future honors.
Former senator and president Harry S. Truman returned to the Senate and was honored on the occasion of his 80th birthday. The Senate had recently modified its rules to allow former presidents to address the body, a rule change once advocated by Truman during his time in the Senate. Twenty-five senators rose in turn to celebrate his career and birthday. When it was his time to respond, Truman was choked with emotion. Referring to the Senate’s newly extended privilege, he said, “I’m so overcome that I can’t take advantage of this rule right now.”
Senator Thomas F. Eagleton of St. Louis became the Democratic vice presidential nominee for the 1972 election. A month later, however, presidential nominee and South Dakota senator George McGovern replaced Eagleton on the ticket with Sargent Shriver due to health concerns.
John C. Danforth of St. Louis became chairman of the Senate Committee on Commerce, Science, and Transportation, serving until 1987.
Senator Christopher "Kit" Bond of St. Louis became chairman of the Senate Committee on Small Business and Entrepreneurship, serving until 2001.
Jean Carnahan was appointed to the Senate to fill the vacancy caused by the death of her husband, Governor Mel Carnahan, who was posthumously elected a month after he was killed in a plane crash while campaigning. Senator Carnahan, Missouri's first woman senator, served until November 25, 2002, when an elected successor, James M. Talent of St. Louis, took office for the remainder of the term.
Senator Claire McCaskill of Rolla, the second woman to represent Missouri in the Senate, received her first Golden Gavel Award for presiding over the Senate for 100 hours in a single session. She received a second Golden Gavel on September 26, 2008.