The Democrats in marginal districts who are patting themselves on the back for taking the "safe" vote by voting no on health care reform are fooling themselves, and in a great many cases dooming themselves in the next election.
If the part of the electorate that strongly favors you drops by 10% (or more) in the next election, do you really think you can win a competitive race?
And does not helping your party and your President deliver health reform help you or hurt you in turning out the Democratic vote? ...
The Democrats who oppose health care reform are also hurting themselves in a lot of different ways besides depressing turnout:
They damage the brand of the Democratic Party as an effective party that can get things done
They hurt the approval rating of the President they will need campaigning and raising money for them next year
When Democrats like the President nationally are making the case as why Dems in 2010 deserve re-election, they will use the passage of health care reform as their number one selling point, leaving you on your own to explain why you deserve re-election
They lessen their ability to raise money from all those Democratic activists and interest groups who care about health care
They dampen the enthusiasm of volunteers back home (This is virtually guraranteed. Several callers to Mario's show have said as much.)