I've pretty much thought that it's that Obamacare isn't front-and-center any longer. Most people can't sustain fury every day. When they were having their faces rubbed in it--every day--naturally his numbers tanked.
But fury comes to be replaced by sullen anger, and that's all it'll take to drag down the communist-democrat party in November. I've read a great deal of analysis on the opposition to the Obamacare horror's roots, but one item I believe most pundits are missing is that the majority of the electorate who have been, and remain, solidy opposed to what's been imposed upon them are going to vote against the Dems out of sheer orneriness. Orneriness well earned by the Dems, natch. Never mind the hideous substance of the law, or any of its future effects; the electorate will stay angry because Pelosi/Obama/Reid and their mob syndicate posing as a political party did what they wanted to do in spite of the pretty-much-shouted will of the American people. That alone is enough.
I don't believe for a second we're going to gain seats in just the 20s in November, as is so often reported by "thoughtful" (read: timid) election projection web sites. I suspect we'll be seing Dems thrown out and conservative Republicans voted in in numbers surpassing 1994. That's my gut feeling. Dick Morris is much closer to reality on this that the "gain in the 20s" people.
As for Obama--it's one term, baby. No President recovers from a fall like this. He's lost 2/3 of the independents in some states and 3/4 in others, and they're not coming back, no matter what the economy does. They know he and his cabal disobeyed the most vehemently expressed wish of the American people, and that's all they need to know.