I can't say this makes a lot of sense to me unless all the other candidates follow suit. Otherwise, it seems like a "cut off your nose to spite your face" strategy. David Shuster and Chuck Todd of MSNBC discuss:

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AP: Barack Obama, John Edwards and Bill Richardson have withdrawn from Michigan's Jan. 15 Democratic presidential primary.

The three filed paperwork Tuesday, the deadline to withdraw from the ballot, said Kelly Chesney, spokeswoman for the Michigan Secretary of State's office.

All of the Democratic candidates already have agreed not to campaign in Michigan because it broke Democratic National Committee rules when it moved its primary ahead of Feb. 5. The decision by Obama, Edwards and Richardson undercuts the validity of the contest.

Other Democratic candidates had until the end of the day to decide if they'll stay on the ballot.

UPDATE: Per MSNBC, Joe Biden has opted to pull out as well.

UPDATE #2: Dennis Kucinich has issued a statement asking to be left off the ballot as well.