There are 33 United States Senate seats up for re-election in 2012 and since 2006 was such a huge year for the Democrats, they currently hold 23 of those seats while the Republicans only hold 13.
Already 4 Democratic-caucusing senators have announced their retirement (Bingaman of New Mexico, Conrad of North Dakota, Lieberman of Connecticut and Webb of Virginia). Only two Republicans have declined to seek reelection (Hutchison of Texas and Kyl of Arizona).
