The West Virginia lawmaker died peacefully at a hospital in Fairfax, Virginia, the spokesman says. The cause of death was not immediately known.

Longest-serving US lawmaker Robert Byrd dies, aged 92Senator Byrd was elected to the House of Representatives in 1952, becoming a senator seven years later. As a young man, Mr. Byrd was for a brief period a member of the white supremacist group the Ku Klux Klan and also joined Southern Democrats in an unsuccessful filibuster against the 1964 Civil Rights Act. He later apologized for both actions, saying that intolerance had no place in America. In his later years as a senator, Robert Byrd became a champion of civil rights. He was also an outspoken opponent of the Iraq war and warned against a build-up of US troops in Afghanistan, winning a record ninth term in the Senate in 2006.

His death is not expected to change the Democrats' current majority in the Senate. West Virginia Governor Joe Manchin, a Democrat, is expected to appoint a Democrat to serve the remainder of Mr. Byrd's current six-year term, which expires in 2012, Reuters reports.

Clinton Impeachment

"George W. Bush's favorite Democrat"Sen. Byrd's most controversial action in the Senate was his decision to support the conviction of President Bill Clinton at his impeachment trial and to use his influence to persuade other Democrats to do likewise. Byrd's efforts led to the defection of a coalition of Democratic conservatives and self-described "independents," among them Ben Nelson of Colorado and Joseph I. Lieberman of Connecticut from the embattled President's side, making possible Mr. Clinton's conviction, by a margin of one vote, on Feb. 16, 1999. Mr. Clinton thus became the first U.S. president ever removed from office via impeachment. (In 1868, Andrew Johnson-the only other president ever impeached and like Clinton a Democrat facing a Republican Congress-was acquitted by one vote. Richard Nixon, facing impeachment, resigned instead.)

Bitterness over the impeachment would affect the 2000 election. Senator Lieberman would be repudiated in his state's Democratic primary and would win another Senate term only by running as an independent with substantial aid from the Republican Party, which actually provided more funds to his campaign than to that of its own nominee for his seat. President Gore would spend much of the campaign fending off Republican efforts to impeach him as well. GOP opposition to Gore was sufficiently powerful to prevent the confirmation of anyone to replace Gore as VP, meaning that if he, too, had been removed from office, the Republican speaker of the House, Dennis Hastert, would have succeeded to the presidency, the first time in U.S. history the office had changed partisan hands without an intervening election. (The closest parallel would have been that of Andrew Johnson, a Democrat, had run with President Abraham Lincoln on a Union ticket in 1864.) Lieberman, running as a Republican in 2006, having joined the GOP after an unsuccessful attempt to mend fences with the Democrats and run for that party's 2004 presidential nomination, would lose to Democratic challenger Ned Lamont in a race whose most memorable commercial would be nicknamed "Hop, Frog," featuring Sen. Lieberman as a frog leaping among lily pads labeled "D", ""I" and "R".

Byrd, by contrast, would survive relatively unscathed, calmly enduring his being tagged by both parties as "George W. Bush's favorite Democrat" after Bush's narrow victory over President Gore and running-mate Sen. Patrick Leahy of Vermont. In the evenly divided Senate which emerged from that election, he would wield extraordinary power due to his combination of seniority and personal influence. As recently as 2009 he was a senior Democrat on the powerful Appropriations Committee.