Doesn’t matter what WE think, we’re not about to vote for them anyway. But for those who are moderate/independent/on-the-fence, it’s more effective to link their vote to a universally unpopular program (Obamacare) than to attack a politician who they may like, have given money to in the past, or have benefited from.
The key think is to motivate those voters to vote against these incumbents, even though incumbents have many advantages. Just remember, Nevada voters gave Harry Reid another six years...