When the House-passed bill arrived in the Senate on February 26, 1964, Majority Leader Mike Mansfield placed it directly on the Senate calendar rather than refer it to the hostile Judiciary Committee. On March 9, when Mansfield moved to take up the measure, southern senators launched a filibuster against the bill. The Senate debated for fifty-seven days, including six Saturdays.
To cut off debate required a two-thirds vote, or sixty-seven senators, and since southern Democrats opposed the legislation, a substantial number of Republican votes would be needed to end the filibuster. Minnesota Senator Hubert Humphrey, the Democratic whip, who managed the bill on the Senate floor, enlisted the aid of the Republican minority leader, Everett M. Dirksen of Illinois. Dirksen, although a longtime supporter of civil rights, had opposed the bill because he objected to certain provisions. Humphrey therefore worked with him to redraft the controversial language and make the bill more acceptable to Republicans. Once the changes were made, Dirksen gained key votes for cloture from his party colleagues with a powerful speech calling racial integration "an idea whose time has come."
This coalition effort finally enabled the Senate on June 10 to vote 71 to 29 for cloture, thereby limiting further debate. On June 19, the Senate passed the most sweeping civil rights legislation in the nation's history.
For further reading:Mann, Robert, The Walls of Jericho: Lyndon Johnson, Hubert Humphrey, Richard Russell, and the Struggle for Civil Rights (New York: Harcourt Brace & Company, 1996)
Whalen, Charles and Barbara, The Longest Debate: A Legislative History of the 1964 Civil Rights Act (Seven Locks Press, 1985).