Certainly not, but they may abstain or vote for a third party candidate. And again, I think it's less about the Dems losing votes than it is about the GOP/Conservative base being 'energized' (cliche, I know) over the healthcare bill. Conservatives were disenchanted with the 8 long years of the Bush presidency and a McCain/Palin weaksauce ticket and lost out in 2008. I think things will be a lot different this election cycle.