Polling suggests that US Senator Nelson (D, NE) has already seen his approval numbers in Nebraska plummet. A Rasmussen Poll suggest his approval numbers are down 30 points and he'd lose to current Republican Governor 61% to 30% if the election was held today.
The reason for the rapid decline is the highly prominently role he's played in the health care debate. He initially opposed the bill for its allowance of abortion coverage and its cost. Then quickly reversed course after cosmetic changes were made. Now he's going public to defend his vote to Nebraskans. That will only deepen the opposition to him by many Nebraskans who are already upset with him.
Will it cost him eventual re-election in 2012? That's hard to say because three years is a long time away in political terms. However, if the problems only grow for the party in power - the Democrats in this case - and I think they will for both things within and outside their control, he should be in trouble in 2012 as well.