Obama's 2014 election strategy will be "If you benefit from Obamacare, it's because of Democrats. If you don't, it's because Republicans screwed it up for you."
That's pretty much been the Democratic narrative on the economy since 2009. "The economy is doing better thanks to Democrats, but if it's not doing that well for you, it's because Republicans stopped us from doing more."
In 2010, that Democratic strategy blew up and resulted in big Republican wins. What Democrats forget is that Republicans had very low approval ratings when they won that year. So high approval ratings aren't necessary.
In 2012, Democrats stuck with it, but Obama framed his re-election on how awful Mitt Romney would be as President and how he was a better alternative. Thus, Obama finished 2 points better than Democrats.
American elections have always been a referendum on the President. If they like the job he's doing, they're with him. If they don't, they aren't. Democrats are ignoring this and have decided that this election will be judged differently. Good luck changing the way the electorate votes.