Washington (CNN)  -- 2010 has opened on an unsettling note for Democrats in the U.S. Senate. Connecticut's Chris Dodd and North Dakota's Byron Dorgan -- two longtime power players in the chamber -- have announced their intention to step down at the end of the year. If history is any guide, the party now faces an uphill struggle to maintain its 60-seat supermajority. Failure to do so could have serious ramifications for President Obama as he tries to look past the health care debate and tackle global warming, ballooning budget deficits and a range of other politically contentious issues. The fight over health care reform has clearly demonstrated that 60 votes is now the minimum threshold for passing major legislation through the Senate. Anything less leaves the majority party at the mercy of a minority increasingly willing to employ the filibuster to grind the legislative gears of the Senate to a halt.
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Democrats need 60-seat supermajority in Senate to get major bills passed
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Sens. Chris Dodd and Byron Dorgan announced this week they won't seek re-election
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GOP targeting vulnerable seats, including those vacated by Obama and Biden
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Flipping could go both ways, with Dems picking up some GOP seats
Dodd's decision to retire, however, is widely believed to be beneficial to Democratic chances in largely liberal @placeholder.