OBAMA TO GIVE UP SENATE SEAT ON SUNDAY…. It seems strange, but technically, Barack Obama is still a sitting senator. In fact, in an odd twist, when Congress reconvenes for a lame-duck session, Obama and Joe Biden can still vote on legislation while working on their transition in a competing branch of government.

Obama has indicated that he’s not quite comfortable with this arrangement, which seems to touch on some serious separation-of-powers issues. With that in mind, Obama will officially give up his Senate seat on Sunday. Subscription-only Roll Call reported:

“It has been one of the highest honors and privileges of my life to have served the people of Illinois in the United States Senate,” Obama said in a statement on Thursday. “In a state that represents the crossroads of a nation, I have met so many men and women who’ve taken different journeys, but hold common hopes for their children’s future. It is these Illinois families and their stories that will stay with me as I leave the United States Senate and begin the hard task of fulfilling the simple hopes and common dreams of all Americans as our nation’s next President.”

It is unclear when Vice President-elect Joseph Biden, who was elected in Delaware to a seventh Senate term last week, will resign from his seat.

Obama’s resignation will take effect just as Congress is returning for a weeklong lame-duck session.

And speaking of Obama’s departure from the Senate, what’s the latest on the search for his replacement? Illinois Gov. Rod Blagojevich (D) has created a committee to vet possible replacements. Roll Call noted several of the likely candidates, including Reps. Jesse Jackson Jr. and Jan Schakowsky, state Comptroller Dan Hynes, state Veterans Affairs Director Tammy Duckworth, former state Senate President Emil Jones, state Sen. Kwame Raoul and marketing consultant Dan Seals. For what it’s worth, I’ve also heard state Attorney General Lisa Madigan’s name on rumored short lists.

Chris Cillizza has a rundown on the chances for all of them.

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.