Personally, I would have liked to have seen Lott stay in his position.  It would have been great for the Democrats.  Sort of like the gift of Dick Cheney that keeps on giving…

The majority leader of the Senate is elected by the majority party in the Senate when the term begins.

http://www.senate.gov/artandhistory/history/common/briefing/Majority_Minority_Leaders.htm

The Democrats could not forcibly remove Trent Lott.  Only the Republicans could remove Trent Lott from the majority leadership of the Senate. 

“Political controversy ensued following remarks Lott made on December 5, 2002 at the 100th birthday party of Sen. Strom Thurmond of South Carolina. Thurmond ran for President of the United States in 1948 on the Dixiecrat (or States’ Rights) ticket. Lott said: “When Strom Thurmond ran for president, we voted for him. We’re proud of it. And if the rest of the country had followed our lead, we wouldn’t have had all these problems over the years, either.”[3]

Thurmond had based his presidential campaign largely on an explicit racial segregation platform. Lott had attracted controversy before in issues relating to civil rights. As a Congressman, he voted against renewal of the Voting Rights Act, voted against the continuation of the Civil Rights Act and opposed making Martin Luther King Jr.’s birthday a federal holiday.[4] The Washington Post reported that Lott had made similar comments about Thurmond’s candidacy in a 1980 rally.[5] Lott gave an interview with Black Entertainment Television explaining himself and repudiating Thurmond’s former views.[6]”

http://en.wikipedia.org/wiki/Trent_Lott

Trent Lott did not just resign because of what he said during Strom Thurmond’s 100th birthday party.  The Republicans did not support him after President Bush would not stand behind him.  Speculation about why President Bush did not stand behind him was because Trent Lott could not get his immigration reform through the Senate.

“President Bush distanced himself from Lott’s remarks, telling an audience the comments “do not reflect the spirit of our country.””

http://www.msnbc.msn.com/id/21973397/

This is yet another ridiculous attempt by the Republicans to kill health care reform.