Senate Minority Whip Trent Lott (R-Miss.) will announce at noon today that he will resign his seat by the end of the year, a shocking move sources said was precipitated by a desire to spend more time with his family and a general fatigue of Congress.Lott, who made a stunning return to the GOP leadership just a year ago, made the decision over the Thanksgiving holiday. One well placed Republican source said Lott isn't sick nor is he facing any ethics charges but rather wants to spend more time with his grandchildren."He wants out," a Republican said. "He's fed up."Lott had entertained retiring in 2006 but opted to seek another six-year term in the wake of Hurricane Katrina, which devastated his state. He had indicated he had no plans to run for another term in 2012.The move throws open the GOP leadership field, which is led by Minority Leader Mitch McConnell (Ky.). There's no doubt a cast of ambitious Senators will look to jump into Lott's Whip post, first among them likely to be Conference Chairman Jon Kyl (Ariz.), a close Lott ally.Beyond Kyl, other possible contenders to succeed Lott as Whip include Sen. Lamar Alexander (Tenn.), who lost a bid for the post to his Mississippi colleague by just one vote. Also, Conference Vice Chairman John Cornyn (Texas) and Chief Deputy Minority Whip John Thune (S.D.) could be candidates.Tom Ingram, chief of staff to Alexander, said his boss is talking to Senators and is taking a hard look at both the Whip post and the GOP Conference slot if that job becomes available. Ingram said Alexander "isn't ruling anything out.""He's been encouraged by a number of Members to consider the Conference position if Kyl pursues the job as Whip," Ingram said Monday. "He hasn't ruled either out. [It all depends on] if he feels he can make a constructive contribution to the Conference, a postive difference to the Senate and the country."Sens. Richard Burr (N.C.) and Kay Bailey Hutchison (Texas), now the Policy Committee chairwoman, also could be interested in the Conference chairmanship. Sources indicated that calls already are under way to lay the groundwork for the ensuring leadership elections, led by Alexander and Kyl.Politically, Lott's resignation could put another Senate seat in play and further complicate GOP hopes of holding their ground at 49, let alone recapturing the majority.It was barely two weeks ago that Sen. Thad Cochran (R-Miss.) announced he would seek another term in 2008, giving Senate GOP election strategists a pleasant surprise as they prepare to defend 22 seats next year. Lott's resignation will create the second scenario of the cycle where Republicans are defending two Senate seats in one state, Wyoming being the other.Mississippi election law was not immediately reviewable, but it is likely that Gov. Haley Barbour (R) will appoint a replacement for Lott. That replacement will likely have to run for the remainder of Lott's term in 2008, creating another seat for the GOP to defend where previously one wasn't even up for election.Although Lott's replacement could run as a virtual incumbent, the Democratic Senatorial Campaign Committee's deep coffers could make going after Lott's seat an attractive proposition.